The U.S. Mint has been trying to promote the use of $1 coins, offering free shipping to those who “purchase” large quantities of the more durable, more efficient currency.

Some credit card banks promote the use of their cards by offering frequent flyer bonus miles as a reward. The more you purchase with those cards, the more bonus miles you collect.

If you already see where this is going, then you’re a step ahead of the banks, the airlines and the mint — all of which were caught off-guard when they discovered people were exploiting this legal loophole.

The Mint figured out what was going on when some consumers started ordering large quantities of $1 coins, then depositing them in their local banks which, in turn, returned them to the Mint — still in their original wrapping. Now they’re closing the loophole.

But for a while there, a few canny consumers had taken advantage of this combination of offers to rack up enough miles for free flights all over the world. The process was simple.

Step 1: Purchase $20,000 or so in $1 coins from the mint using the rewards card, getting lots of bonus miles.

Step 2: Deposit the coins in the bank, using that $20,000 to pay off the balance on the credit card before accruing any interest.

Step 3: Repeat steps 1 & 2 until you’ve got enough frequent flyer miles for a first-class ticket to wherever it is you want to go.

National Public Radio’s David Kestenbaum and Robert Benincasa reported on this trick back in July in a report titled “How Frequent Fliers Exploit a Government Program to Get Free Trips.” Mint spokesman Tom Jurkowsky explained that the mint has imposed a limit of 1,000 coins every 10 days in an effort to close the loophole:

“It’s not illegal,” he said, “But it’s an abuse of the system. That’s not what the system was set up to do. The system was set up to promote the use of dollar coins and we are simply trying to do the right thing here.”

I bring this up because right now the same strategy that these “travel hackers” employed to acquire free flights all over the world can be employed by the U.S. government to make desperately needed overdue repairs and upgrades to our aging infrastructure and to end the deadlock crippling our economic recovery due to a lack of overall demand. Uncle Sam has a similar opportunity to use free money to create jobs and to attend to these red-alert repairs while at the same time helping to erase the short-term budget gap created by our current massive unemployment rate and the contraction that followed the Great Recession.

The government can’t get free frequent flyer miles, but it can get something even better — free cash. And if that sounds too good to be true, let me assure you that it’s even better than that. It’s actually free money plus free money — it’s free money being pushed on the Treasury by those desperate for the privilege of lending the Treasury free money.

The U.S. federal government, right now, can borrow money at a negative interest rate. Here’s the proof I’m not making this up:

Understand what this means. A negative interest rate isn’t just borrowing interest-free. It’s getting paid to borrow. It means earning interest on every dollar borrowed.

Why is this happening? Ask the bond market, that’s who’s doing this. If you believe in free markets, then you have to listen to what those markets are saying, and what those markets are saying right now is that they want the U.S. government to take their money. They’re begging the U.S. government to take their money.

Fact is there’s nowhere else to put it. Equities are terrifying just now and what investors want is safety. In this world, that means mainly one thing: U.S. government debt. Despite this summer’s shenanigans over the uniquely American invention of the “debt ceiling,” and despite the presence of a faction in Congress eager to concoct an unnecessary default, the bond market doesn’t believe that such a default is a credible threat and it desperately, urgently wants the U.S. Treasury to take more of its money.

That makes sense. Imagine you’re sitting on $20 billion. What do you do with that right now?

Maybe your plan was to invest it in a growing business, but with the global economy in the doldrums, there’s no point in doing that just now. You could invest that money in building a new factory to make more widgets, but you’d lose money on that deal because right now consumers can’t afford to buy all the widgets the factory would be producing.

You could put the money in the bank where it would earn interest in something safe and solid like housing loans, but the housing market is also swirling around the drain these days. Plus you already tried that and you got burned. If you’re the kind of person (or Chinese government) with $20 billion lying around, then odds are you already had a ton of money in some kind of mortgage-backed securities four years ago and that did not end well.

You can’t stuff $20 billion in your mattress or stick it in a giant piggy bank because inflation — even at its current modest rates — would eat away at it.

What you need is somewhere safe to put your money until demand rebounds to the point where it starts making sense to build that factory. It doesn’t matter if you’re not making money with your money until then, at this point you’re just trying not to lose it — or trying to find a place to put it where you won’t lose as much of it as you would by sticking it in the mattress.

And that means lending it to the U.S. Treasury.

So right now the bond market is all, like, “Please borrow this money!” And the U.S. Treasury is, like, going “We’ve already got enough debt, thanks, no.” And so the bond market is like, “Come on, please.” And the Treasury is like, “No, seriously, I am not paying any more interest to borrow more money.” And so the bond market goes, “Just take it for no interest then.” And Treasury’s like, “Uh-uh.” So the bond market is all, like, “Fine, whatever, we’ll pay you to take it — we’ll earn negative interest on it, just please, have mercy on us and take our money!”

That’s what this means.

On the one hand, this is very good news for the U.S. Treasury. The chance to earn money by borrowing money is a sweet, sweet deal. It’s a nice perk for being a sovereign top dog and to be offered such a deal — the kind of terms that make Greek, Irish and Spanish officials weep with jealousy.

But on the other hand, such a deal only arises because the global economy is in really, really bad shape. The U.S. Treasury is being offered free money to take more free money only because that money, right now, can’t be invested anywhere else — it can’t find any other more productive use, any way to do all those things it ought to be doing in a healthy, growing economy.

So the key for America is to seize this opportunity and to use it to help get things back to the way they ought to be — back to a healthy situation in which investors are able to find better, more productive uses for their money than begging the Treasury to hold it for them.

Right now we’re in a catch-22. Businesses don’t want to hire any more workers until consumers look like they’re willing and able to buy the goods and services those new workers would produce. And consumers won’t be able or willing to buy such goods and services until those businesses start hiring more workers, because buying more stuff is not a smart move if you’re worried you might lose your job and not be able to find another one in this labor market.

So we’re locked in a holding pattern.

The bond market is begging the U.S. Treasury to take its money because the U.S. government is one of the few actors able to break this impasse. Consumers can’t do it — they’re waiting for hiring to pick up. Businesses can’t do it — they’re waiting for consumer spending to pick up.

But the government can start doing both — it can start spending and hiring, thus increasing the demand for businesses to start investing in those new factories and increasing consumer’s capacity to buy the goods those factories will produce.

“Gaah!” cry the deficit hawks. “Government spending bad!”

Aversion to debt is a prudent and responsible principle. But it would be foolish to make it an absolute principle — that would rule out any leveraged investment, no such thing as a mortgage or a business loan. But more importantly, when interest is negative the normal rules do not apply. It may be “fiscally responsible” to refuse to borrow at even very low interest rates, but when those rates become negative, it is fiscally irresponsible not to accept the free money you’re being offered for accepting more free money.

“Take this free money,” the bond market is saying.

“No,” say the voices of fiscal responsibility. “Debt is bad.”

“We’ll pay you to take this free money,” the bond market says. “We’ll give you money to borrow our money and you won’t owe us a penny of interest.”

“No,” say the voices of … well, if they keep saying “No” at that point, then it would be nonsense to keep calling them the voices of fiscal responsibility.

Those who claim to believe in free markets cannot continue to claim such belief if they refuse to listen to what the free markets are demanding. And right now what the bond market is demanding — what it is screaming for at the top of its lungs — is more U.S. government spending.

I appreciate the general ideological principle that weighs against government spending, preferring to leave the decisions on what and where to spend to the free market and the private sector. In an ideal context, any public project ends up hiring workers away from their productive roles in the private sector. That means, during full employment, that the government’s decision to build another Hoover Dam would mean building that dam instead of building more houses, or cars or iPads or more of whatever it was the private sector was employing those workers to make.

But this is not an ideal context and we are far, far, far from full employment. Right now, the private sector has no use for those workers and some 14 million of them — of us — are sitting on the sidelines, unproductive, desperately eager to contribute but not allowed to do so.

And right now the free market — the private sector itself — is begging the government to put that army of unemployed workers to good use.

We can do that, right now, for free. For less than free.

Anyone who says we shouldn’t doesn’t really believe in free markets.