I put my arm out as a brace. He puts his forepaws on my arm. This is phase one. I tried to shape this in other places, but he just didn't "get" that he was supposed to put his paws on my arm. Kitchen table--first try, perfect!
Phase two is to shape him so that his head goes between his front paws and he is rewarded under the braced arm. Phase Three is to fade the arm and have the dog do a stretch on the floor. Fun stuff.