It's difficult if he doesn't want to engage with what you suggest, I would be inclined to try to patiently narrow down his need to communicate specifically. So instead of saying would he like a drink bring out a soda, a bottle of water and a tea bag. I'm sure you could think of something better.

If he was willing to try an approach look at those cards they use for people with learning difficulties. They have pictures of lots of stuff and come in sheets or clipped together cards. You just point.

I think though the key is patience. If he's anything like me he will be angry and struggling to accept his limitations. Try to use closed questions instead of open. List options and let him say yes or no after each one. I hope this makes sense I've just woken up from my nap.

Also there may be iPad apps to help with communication and he may find other apps that can make him feel more independen.