Strangely enough, I thought of both of them. Elminster's dialogue would be too trying to have to attempt to write, and Rincewind would get in the way too much.

I would suggest Albus Dumbledore, but he's still semi-catatonic.

I'll probably end up with Charles Xavier, and make the rest of the Fellowship (which has only one canonical character remaining) haul his damn wheelchair all over Middle-Earth.