I agree with Rod and Kevinshorses. I'm interested about your timeline though. You say that you can start light riding in the beginning of summer, is that due to the suspensory? If so, then I would be very careful with Parelli games or any other training exercise until then. I am personally not a fan of Parelli, but to each his own there.
There are ways to achieve this with your horse without moving his feet. It sounds strange, but I would start by ignoring him. Your wanting him to like you will be interpreted by weakness through his eyes, what he needs is leadership. Another horse wouldn't feel pity on him because he was mistreated or injured in the past, a good lead horse would have the same expectations from him as they would any other horse. You have the knowledge to know that he has physical limitations, so you can alter the way you work with him. If it were me, I would just spend some time in his stall. Take a book, don't worry about him at all. Spend some time every day, don't give treats or try to bribe him to be your friend. If he is the type to barge right into your space, keep him out, if he stares in the corner, just leave him alone and eventually he will start letting down his defenses.
You can also use feeding time as a training opportunity. The lead horse controls the food. These are both ways that you can begin to work with his trust and attention issues without putting a lot of excess pressure on him physically.
I would probably do as others said and completely restart him as a young horse when the time comes for him to start undersaddle again. Good luck.