I would just let him smoke the dirt until he can get a bit more used to it. Because it seems like if you just try to stop him from smoking completely, it will make a schism between you both that will just be unpleasant and could possibly hinder smoking between you all after that. So I would just let him smoke the dirt, and allow his tolerance to get sorta high, before you start trying to expose him to the chronic. That way, he will be able to enjoy it without throwing up. Good luck! Good lord I'm so drunk.