The way you phrased that kind of makes it sound like just another commitment to be avoided. Wouldn't you need to do something more like "give your friend $1000 in escrow and tell her she should only give it back to you if you run the marathon"?
This depends how trustworthy you are in general, and is definitely an interesting question.
Would Gandhi take a pill which made him 1% less likely to not commit any murders, if it meant receiving a million dollars with no other strings attached?
The answer seems to be, "he would use a Schelling Fence" if that was an option.
