In the annals of the Make-a-Wish Foundation, there's never been anything as big as this.

A five-year-old boy named Miles, who lives in northern California, has leukemia. He loves superheroes, and his fondest wish is to be Batman. So Make-a-Wish put out a call for help from the citizens of San Francisco, where Miles' wish is to be realized in an elaborate set of stunts on Friday, Nov. 15.

They got more than they bargained for — 10,000 RSVPs on the website, and counting. [UPDATE: The number jumped from 7,100 to 8,100 overnight, and hit 10,000 on Tuesday afternoon.]

The plan is for Miles to have an action-packed day around the city: rescuing a damsel in distress on a cable car, capturing the Riddler in a downtown vault, chasing the Penguin around Union Square, and finally receiving the thanks of a grateful mayor and police chief on the steps of City Hall.

Volunteers were needed to form large, appreciative crowds to witness Batkid's deeds, and urge him on in all those locations; organizers say they had no idea they'd be getting this many sign-ups. It may not be a world record for largest flash mob, but it is certainly the largest event the foundation has ever put on.

A number of supporters from around the U.S. have told Make-a-Wish they'll be flying to San Francisco just to participate. "As soon as my husband and I heard about this on our radio, we got online and ordered our airline tickets," wrote a retired teacher from Akron, Ohio. "This is the first time we've ever heard of anything like this."

Foursquare will be letting participants check in to "Gotham City" on the day. Several Facebook users set up a Batkid page. The Penguin is taunting Batkid on his new account, run by award-winning social media agency Clever Girls Collective:

Other Batman-themed tributes to Batkid are in the works. It's possible Miles may end up with a comic book from DC Comics detailing his exploits — and a musical theme of his own, offered by Dark Knight Trilogy composer Hans Zimmer.

Image: Make-A-Wish, Greater Bay Area