From his body language (his stance, the way his ears are pointed forward in curiosity and the interested look in his eyes) I think it will be possible to tame him, but it could take a long time. The wide eyes and 'pulled back' body, suggest that he's very frightened. For this reason I suggest that you don't trap him, but continue to feed him and provide him with shelter.
When you feed him, talk softly to him. Try to spend just a little time with him during the feeding routine, to get him used to your presence. Don't try to touch him.
If you have to put the food down and walk away, and he comes for it in his own time, continue doing this. Maybe try to feed smaller meals more often, so that he needs to visit your garden frequently.
Very slowly, he'll realise that you are the source of good things, and will allow closer contact. Always let it be on his terms. Don't push him too fast.
Eventually, he'll be a great, loving cat.