Well, i think it's an awesome idea!!! look, sex can be whatever you want it to be- no ground rules. Because you're friends, exercise your fetishes all you want and do whatever you want because you have no emotional attachment whatsoever. have fun! It's a win win situation!Just also be there for them as a friend, don't be their whore is all i'm saying. it's a chance for both of you to improve yourselves in bed. Keep in mind that Most people aren't open to this kind of relationship, so make it look as attractive as possible to start with. that's all man:)