We've been looking at the best ways to deal with finances, and we are thinking of adopting Kickstarter's model. This way we wouldn't hold the money itself - we would direct all transactions to the bank account of the partnered lobbying / advocacy firm of a cause.
Do you get to choose which cause you are donating to? Either way, you would basically need to have that organization directly debit the donor's account. Sounds tricky.
http://www.plainsite.org/issues/index.html?id=1