Taken to the extreme, this sounds a little bit like selling your marrow or blackmailing the recipient. That might not actually be a bad thing, if the money were sent towards valuable charities. But people don't like the sound of that, so your way is probably better. If I am asked to donate, I'll be sure to drop hints to the recipient that I signed up because I wanted to make the world a better place, and that they should consider doing the same.