WikiLeaks, which publishes anonymous leaks of secret material (most recently 250,000 previously secret US embassy cables) still has a trick up its sleeve. In the last few days its sources of funding have been gradually cut off. MasterCard, PayPal and now Visa have all suspended payments to the organsation and founder Julian Assange has been remanded in custody in London without bail (so far).

However there remains one source of funding so far untouched, and that is a small startup, Flattr, created by Peter Sunde, co-founder of torrent site Pirate Bay, who has been reminding Twitter users today via his personal Twitter account that it’s still possible to “help” Wikileaks.

Now, any site at all can use or incorporate Flattr – a sort of Digg or Facebook ‘Like’, but with money attached. But it is significant that on this day, when other sources are slowly shut off, a tech startup remains a revenue source for Wikileaks. Although there is no Flattr button on the infamous “Cablegate” pages. Nor is Flattr listed as a supporting partner and there is “no official association whatever”, according to Flattr, with Wikileaks.

Here’s how Flattr works:

Users can “Flattr” content by setting up a Flattr account which sets a a monthly fee — a minimum €2 — that they are willing to contribute for any kind of online content. When the user finds something they like that has a Flattr button, they can click the button to “reward” the content provider. At the end of the month, the user’s monthly fee is split equally among the holders of the content that they “flattered”. Although Flattr is currently in beta and an invite is required to set up an account it is already in use by two major German newspapers, completely unprompted: taz.de and Freitag.de.

WikiLeaks has been using Flattr since August, and received well over 3,000 Flattr donations for its Afghanistan War Diary – but the amounts of cash involved remain unknown.

Flattr does not need Paypal to distribute payments – so long as it can verify an account holder’s identity to comply with anti-money laundering and KYC (“know your customer”) requirements, funds can be transferred via bank transfer or cheque. However, Flattr, which also works with newspapers many of them in Germany, is not confirming if it is doing this for WikiLeaks as this is considered client confidentiality.

Wikileaks could well have hit on an unstoppable model via Flattr, which also won the recent Europas award for best new startup in Europe, 2010.