You have to take baby steps, an inch at a time. Okay he is good three feet away, let's go two. Fine with two, go in for one. Take all you can get for free and don't get into a fight with him. It may take months, but
If you are worried about him striking, and have a heavy Baker Blanket(or other heavy winter blanket) you can use that as protection. Put it over his head, and instead of putting it in place over the back of the horse, turn it around so it hangs down in front of his legs. Then lead him up so that he is stepping on the blanket. That way, if he goes to strike, he is going to hit the blanket, and since he is holding it with his other foot, it should block it.
After several days of attempted desensitization, if that is what you choose to do, and he doesn't get better, you may want to try a calming agent.
Another method we use on all of our youngsters to start, also to keep us out of striking distance, is a clipper stick. It is a set of clippers taped to a long, light pole. Every day on our youngsters, when it is time to start that work, we go in for a few minutes with the clipper stick on, and work our way up to petting them with it. Sometimes it takes only a couple times, sometimes it takes a couple weeks. We go in, with them on(the clippers don't cut), they are loose in thier stall, and we move it in the space around them, and slowly work our way to them. We make these sessions short to begin with, and quit at the slightest "Win".
It may seem hopeless, and frustrating, but just keep going. Leave your emotions out of it and don't get mad. Do a little each day.