This is exactly what stickk.com does. (Combination of "stick" and K for contract.) You can either give money to a friend, a random charity, or an anti-charity, like the American Nazi Association. I haven't tried it myself but it seems interesting. The problem is I'm not motivated enough to fill out $30 mail-in rebates, so I don't see how I'd be motivated enough to not lose $30 to a friend/charity. I guess I'm not willing to risk an anti-charity, and more money would just be too much.