What can I do with an overly submissive dog?

I recently adopted an 11 month old male Jack Russell Terrier. If I had known he was this submissive I probably would not have adopted him (nice of the lady I got him from to inform me...NOT!), but he's here now and I need HELP! I have another dog (German Shepherd) with whom he gets along very well. This dog is so submissive that he literally curls himself up into a tummy revealing ball and urinates on himself. The urination has gotten better since I have eliminated talking to him, and controlled his water intake, but he continues to turn himself inside out when asked to to something he doesn't want to do - like go outside in the morning to pee. I squat down next to him (not lean over) and gently pull on his collar to get him to go outside. Sometimes he will follow my other dog either in, or out. I have the same problem having him return inside. Once in, or out, he is fine. Our routine is the same every day - so there is no element of unpredictability for him. He also does this in other situations like when it's time to go to bed, so it's mostly "transitions" I guess. It's very frustrating and I'm getting tired of cleaning up the pee dribbles. I have been ignoring him when he does a submissive roll and it has improved. I cannot ignore him when I need him to go out to eliminate - or he eliminates in the house. I spoke to the lady I got him from (once I realized the problem) and she said that's just the way he is - to give him TREATS when he does it. So I think the behavior has been reinforced by using treats and coddling. Will I EVER get him to stop? HELP!! Thanks.