Probably the same way you'd promote any other site. Post it on fan pages, create a fan page for it, convince some dude with a lot of reputation and posts on a related forum to post a thread about it, make your own thread on hundreds of related forums for it. Make a video for it on youtube, and juice it with views.
There was one guy, can't remember his name, I think it was satyr85, who created a thread here for his adwords voucher gig, even giving people here free sample vouchers. I'm sure it brought him a ton of business.