How much have you had to pay beeminder?
How do you make payments (escrow, credit card, PayPal, etc)?
Is it a non-profit?
It seems like this would be a great opportunity for a non-profit. Although it may reduce the incentive a bit. I expect it will be psychologically similar. Especially if the non-profit overhead is something like 10%. You are effectively losing 10% of what could have gone directly to your non-profit of choice.