I do not remember who gave me this advice, or which thread it was, but it was a good alternative to the alpha roll. They said if you are having submission problems with a dog, make them work for everything. Make them sit for their meals, make them sit before they go outside, etc... Let them know that you have control over every part of their life. Of course, with this dog, it isn't yours, so I would just stick the humping problem out. He's probably just nervous. I would just say No and redirect his attention.