When your pup first did a fire-jet when you came home, your instinctive reaction was that it was endearing. However, that impression wore off long ago. Aside from the hygiene implications, what really irks you is that the rolling over and piddling is a very real reminder of the dog's submissiveness.
You hate to think that there's even a possibility of the dog being so intimidated by your that he wets himself. Unfortunately, you seem set on a vicious circle. You come home, the dog rolls over, you bend down to pet and reassure him, and he piddles.
How to break the cycle?
Minimize the risk of piddling occurring in the first place, by not getting the puppy over excited when you come home, and making yourself less of a threat to him (by kneeling down and not staring him in the eye.) If you are in the position of having a dog that regularly piddles, then stop him getting over excited, build his confidence, and use distraction techniques in order to eliminate the problem.