Ooh, I've done this one before (at the girl's suggestion as well) and it turned on the lady I was with a LOT. I honestly never considered it to be anything too unusual or *needing* compensation - I certainly enjoyed myself and she did too, which is forever the main thing when playing sex games. Then again, all the ladies I've been with have wound up being fairly adventurous (or maybe I inspire that in them - either way, it works out to the same thing.) It's always been my policy to do whatever the girl wants in bed, and that's pretty much always been reciprocated.
