Well, one thing you could do is politely ask him to play another character if the character ends up being that big of a problem.

You say he has an AC of 26, but what about his touch AC? If it's low enough, you could target that with certain abilities/spells instead.

Also, for a character who is level 11, his reflex save absolutely sucks. Targetting his reflex saves with AOE effects could be nice.