I totally agree with Rios and Kevin.
My horse would not want to pick up one of his back feet and while at my parents breeding farm while I was injured, out came the grain bowl to try and bribe the horse!
Not in my posession.
After he arrived to me, it only took a week or so before he was picking up his rear feet nice and easy. Now he has it waiting for me.
It was really simple to accomplish this.
Basically all I did was use a long lead line - mine is 14 footer from CA's online store, but any longer line will work.
Since tieing the horse was also an issue at first I just started out by going to each foot and holding contact with the lead line. I asked in the normal fashion for him to pick up the foot. I also use a voice command "foot"
When my horse was picky and not wanting to allow his bcak feet to be picked up I just took the lead line and went through the tie ring and did not tie it off. I left slack in the line and only held it with light contact. When I would ask for the rear foot and the horse got antsy or refused I just tightened the contact with the lead line.
After a week or so he figured out the wrong decision on his part (refusal to pick the foot up or not allowing me enough time to pick his feet) was hard. When he did allow me to do the necessary things I would release the pressure on the lead. Thus, the right decision was "easy".
When my horse arrived his feet were not in the greatest condition. It was, and always is a vital part of horse care to pick feet and tend to them daily.
This horse your speaking of may have an issue with his feet being messed with being he/she is a rescue, but in my personal opinion with consistensy and daily work on the hoof picking and hoof handleing these things can be over come.
Hope this helps out. It was really important for me to work on this because I did not want my horse to have a bad time/experience with a shoer. It was bad enough that the grain was used as a bribe method. That is something that I just do not do.
Best of luck on this one!