If he really is that bright and you cannot change his ways, nor do you want to lose him but you still want your code to be documented and commented then my suggestion would be to let a less experienced developer do the documenting and commenting for him.
Personally if I were a star developer I would feel prettiy foolish if someone else was made to comment my code and I would start to do it myself eventually. In the meantime while that does not happen the less experienced developer may learn a thing or two.
