I love the idea of losing weight with a donation-based pledge behind it. I think any goal that keeps you motivated is good, but this may help connect you to that baseline human instinct that we all take for granted - the free, plentiful availability of food for sustenance. Not merely a cheesecake (like you've mentioned and has sadly made my mouth remember how good cheesecake tastes) but just your everyday caloric necessity that so many in every community go without.
I admire you and wish you much good fortune in your weight loss with a message!