Fear is going to be a limiting factor and can actually result in additional injury like a self fulfilling prophecy. A person can only deal with their fear from withing; nothing you can do will change that. At this point, he will have to work his own way through the process and the best thing you can do is be supportive and encouraging. Push without being pushy. As Shredlife said, for many people, an injury is a bit of wake up call to do things smarter.
A quote from an old movie "fear causes hesitation".
I'm just rehashing on this a bit but it's always good to get multiple viewpoints. I see more people, usually newer riders, get hurt by that brief moment of panic right before the rail or jump. It's hard to explain but a good example of this is a beginner going down the run too fast and they panic and fall to stop, we see it all the time on the lifts. That's what your friend is going to have to overcome. If he has the skills, then he can do it he just needs to calm his brain down and realize it was just one bad crash. We've probably all had that ONE crash that really took it out of us. Personally, if I go down hard I have to get right back up and hit it again as soon as possible so I don't overthink it.
So, in the case of the OP's friend. I know you said he is scared of the most basic features, but it might help him a lot for you and whoever you ride with to tone it down and just hit the basic stuff all day. Mess around on a progression park type feature and he may see you do it easy enough that his confidence increases to the point he'll want to try it. A tip I always give kids that are scared to hit something is to take a really deep breath on the way to the feature because again when you panic or get scared you get tense and tense legs are bad, especially on rails. As Snowolf said, push but don't go crazy with it to the point he gets stressed out, it's a mental game he's dealing with right now. Telling him something like "bro you'll feel so much better after you land this again!" is much better than "do it!" or "come on". It could snap him into thinking he needs to overcome it rather than feeling like he can't. If he really doesn't make any effort to hit anything, and won't even consider hitting it when you and your friends encourage him to do it, it's probably not going to change if it's really his personality.
Just out of curiosity, what was the physical injury that caused all this?