Except for the fact that actually implementing this idea through the use of ATMs would be needlessly complicated, I've been a fan of the
"patriot dollars" proposal from Bruce Ackerman for some time now. It's a variant on your standard public financing of campaigns, where each citizen would be given a campaign donation voucher to award to the candidate (or candidates) of his or her choosing.
This article available online at:
http://www.theatlantic.com/politics/archive/2007/06/patriot-dollars/42890/