Actually, how about this:

Integrate with AdBlockPlus. If you pay, there are no ads ANYWHERE. Then, collect donations for EVERYONE. As a blogger, I don't need to have signed up to you, the money is being collected just the same.

Then, begin contacting bloggers and letting them know that they have X in an account with you, and they'd probably want to collect it. That would work. That would work and it would be best done by the AdBlockPlus people.

Edit: AdBlockPlus is (from what I gather on their website) OpenSource and currently lacking a business model. You could probably start working from there on, like AdBlockPlus, Good Samaritan Edition or something