Try using hand signals (sp) Whenever you tell him to sit hold your hand above his nose or whatever. When you tell him to come give him a motion for come. I find it helps a lot. Also when you first start doing come, put his leash on him. Everytime you say "come" give him a tiny tug on the leash. Be sure to give lots of praise when he comes to you!
PS~ I had your pain for a while. Tucker learned sit perfectly and for the longest time he would do nothing else, he still does that once in a while but he seems to be able to understand now. So YES, there is hope!
