It’s a little weird that a friend running a marathon / having a holiday climbing Kilimanjaro / jumping out of a plane / is supposed to compel us to give to charity, but that seems to be the way it is, and it works jolly nicely, so keep it up, everyone.
That said, the idea of sponsoring someone by committing yourself to a virtuous action seems to be far more fitting somehow. And they have a cool name: The DoNation