Hey rob.. you are right. Your son must want to quit himself. You can not force it on him. Im struggling through a cocaine addiction my self. Im doing my very best to stop. But its just so hard. I hate the stuff. I wish i never even attempted to take it.
There is a good app you could reccommend to him called pocket rehab. Its were addicts and ex addicts talk, and help each other out. Its great, plus there is an emergency button that you press if you feel like using and it puts you through to another addict or ex addict and they talk you round in not to use. It does help alot.
Does your son want to stop then?