I suggest you switch to another system, too. NWoD or Call of Cthulhu are both less mechanics-heavy than D&D, so they could be good choices.

However, even in those ones, you should eventually cast spells or use abilities. I'd try to do this the hard way; if he's in real trouble, his character'll think about what he can do (or he will suffer an awful lot of trouble, which can be educational too). Don't be afraid to be too harsh on him; playing a Wizard who doesn't ever cast a single spell is really stupid, and he should eventually realize that.