I commend you for taking him in. These situations always take a LOT of patience! The filly I've been working with (Sour) lately shares a similar story with your boy- except that she did have some contact with people right before I started working with her, and unfortunately...all of that contact was negative, and just about ruined her. When I finally got to her she was agressive and very fearful. That isnt the case with your boy though, and that's fantastic!
Now I want to warn you, I firmly believe in a fairly fast pacedway of going. If you give a horse too much time to think, it will quickly come up with a reason not to do something (ie; trust you, accept you as the alpha, etc) if you keep them on their toes though, they'll quickly become trusting. For over a year I sort of 'danced' around my filly's warning boundaries, never stepping into them because I didnt want to make her hate me more. In reality though, she was beginning to hate me more and more every day BECAUSE I was being so chicken about it. She was bored and I was basically telling her I was too afraid to advance. Once I started making her just a 'little bit uneasy' every time, the rewarded her if she reacted correctly, we began to make a huge amount of progress. I've accomplished three times as much with her in the past two months as I did when I was being too timid about her training for over a year.
That beig said, I would personally recommend the react and reward method. Since you can't really move him at the moment, it might be a good idea to remove your other horses when you're working with him. Once you've done that, bring in his daily rations and make sure he notices you. Before he can begin walking towards you (as he's probably used to by now), approach him at a leisurely walk, with your eyes cast away and your body relaxed into a non threatening posture (loose shoulders, soft back, even breathing) Theres about a 99% guarentee that he will begin to walk away from you, possibly even in a startled manner. Don't slack or quicken your pace. Keep an even distance (atleast two yards or so) and follow after him, just slightly to the side so that he can watch you. I warn you that this CAN take a LONG TIME so plan atleast an hour to do this. AS SOON as he slows his pace AT ALL, slow yours to match his pace. After a while, hunger, curiosity, or maybe even both will win over and he's stop. When he does that, reward him IMMEDIATELY by also stopping. If he approaches you, take a small step towards him also. If he retreats, continue 'shadowing' him. Repeat this until he meets you in the middle for his food. Once he does, congradulate yourself! This is the first step towards establishing your dominance while at the same time being gentle. Carefully set his feed down and leave the ring. Youve made him uncomfortable, gotten him over it, and now you must reward him with removing the thing that makes him uncomforable. You.
Within a few days, he should let you approach him with minimal movement on his part. At this time you should begin staying with him as he eats, and even taking a step or two to the right, then the left, back, and even forewards. It may startle him at first, but he'll get over it. Generally about four-five days into this training, you can now move to the next step. Touching him.
Ok I don't want to type a whole essay right now just incase you don't like this method (many people would rather other ways, and many like this way.) believe me though, it works =] I would LOVE to help you more though in each step. If you like my way of working things, tell me and I'll shoot you some PMs on what to do next when I have a chance, mmk?
GOOD LUCK! And remember, boredom is the biggest killer.
Everyone in your life is meant to
be in your journey, but not all of
them are meant to stay till the end.