Nice to hear you are having some success! I think another dog that walks well on a leash is a great idea. This is also great for socialization. Dogs walk together....it is what they do and they love it. Maybe you could plan some walks with friends or family who have dogs that walk well on a leash. Or borrow a dog for a walk? I am sure soon enough he will be sitting at the door with leash in his mouth ready to go!

PS if you don't already, you should check out some "Dog Whisperer" episodes. I have learned a lot from him :)