To solve this exact problem our model is a bit different. Our daily email features one cause and outlines two charities addressing the problem in a different way.
(Ex Cause: breast cancer Charity 1: Research Charity 2: Support for survivors. You can choose to donate to either of those or if you don't like the cause of the day you can rollover your donation to the next day.
Rollover as much as you like :) We have a few users rolling over 10 days in a row until they hit a cause that resonates with them.