I agree with what others have said...Try giving him irresistible treats and you be the one to feed him, walk him, groom him, at least for awhile. He'll see you more of a caretaker then
Getting on the floor to play with him sounds like a good idea. My maltese is very shy and timid when it comes to new people...She crouches down and tries to run away when someone tries to pick her up. This was really different for us because our first dog, Miko, loves everyone! But we got her when she was 7 months old, so she was like this before we ever got her. All dogs are different, but I think you're moving in the right direction
Try just sitting there holding a treat that he really likes, but not really paying attention to him. He might come over to you and see what you have in your hand.
Good luck, and keep us posted!!