1) Automation. E.g. in the movie Office Space they take shavings off transactions (amounting to a few cents or less at a time) and pool them together. Another example: Auto-rounding up my grocery receipt, etc.
2) Recycling funds. I don't see how this would work in a donation based system where cash-flow is one directional, but it works really well for something like Kiva where funds are returned and the option to recycle is extremely easy.
If any non-profit is to be sustainable, they must put in a HUGE amount of effort to obtain large enough recurring funds or make it really easy to provide funds. Since you are targeting individuals, it's going to be difficult to do the former. The latter will take a little more thought.
All this said, I wish you the best of luck.