I'm thinking that growth spurts can well be part of this problem. Still how to deal with this?
My only thoughts, as well as the diet advice previous, is to continue stall rest, had walk daily (only around a bit, try to keep the speed slower, but try to get a "feel" for what slower speeds are most comfortable with him) Keep a close eye on the swelling, as to not let it increase, feel the area for obvious changes day to day (heat in the area, painful to touch, swelling getting more pronounced, etc) and see how you go for another few weeks..
Does he like stall toys? The wall mounted lick ball-toy seems to have some calming effect on stalled horses, but I cannot say if he will use it, or how effective it may be..I only know that I attempt to get creative with Blue (my TWH), as he is only now 5, and can get a little bored if he is stalled too much. I hand walk, I leave a small radio going, he has a jolly ball and a few stall toys (large stall), and I try to spend extra time with him when the weather gets bad, and turnout is not an option. I play this game with him, simply how to keep his mind occupied, when his legs can't be..