Put a dowel in his arm to control his arm... slice open his hand and place a magnet in it. Now you have lots of possibilities. He can pick a card, hold ropes,coins etc.
They also make facial expressions.. He can look mad or suprised.. Maybe you could show him cards and he looks mad at all of them and he looks "wide eye suprised" at a certain selection.
I suggest you try ventriloquism. I have been practicing for a month and a half, (the best thing is that you can practice ANYTIME). Especially a gorilla would have a deep voice, much easier to do (for me). I had so much fun getting into this new art, I would recommend it to anyone.
Bill Abbott does a whole routine with a chimp and the chimp never talks, only whispers in Bill's ear, VERY entertaining. You don't even need to make him talk..hope this helps..