Pullups will help to relieve the stress of expectation that he should be dry. It is a sign of stress, and the expectation puts even more stress on him.
Then look for stress in his life and find ways to help him express his emotions freely so he doesn't have to let it out in his sleep. There is a section on this in Raising Our Children, Raising Ourselves (yes, I am nuts about that book) that can help you a lot.