Get a damn piercer to do it. While I'm sure your friend has steady hands, he does not know about where to place the piercing to minimize rejection, may not have the curved needle they'd use to pierce with (or the clamps), and frankly as a neurosurgeon likely deals with people who have already been anesthetization, rather then quickly and cleanly putting a needle through someone with feeling.
Its basically like you would let a car engineer change your back lights. Maybe he would do it good maybe not. Its not like he has experience doing it, but then again maybe to him its so easy that he would do it as good as a piercer. If I had to choose though I would rather let an experienced piercer do it. Since piercing stomachs is not something neurosurgeons do on a daily basis.
Well a neursurgeon is most likely the cream of the crop in terms of the people who manage to become one out of all the medical students. Then again, he operates on brains all the time so I'm not sure how much experience he has with belly button piercing. Why not just go to a professional who does it all the time?
ARE YOU SERIOUS? Its a belly button piercing! Lets see, if he can cut open a brain, operate on it and then sew it up with a person still being alive...then yes, yes he can prick some fat with a needle.