I'd be happy to talk to him, don't really know that it would do any good, but feel free to have him PM me if you'd like. I can definately speak to the negative overall effects of smoking a lot of pot long term. (20+ years, 1/8 oz a day) I've been clean about 2 months now, though I do still struggle with occasional drinking which in my heart I know I need to give up as well. There are probably many other's who have "better recovery" than me, but I can definately share with him what 20 years of smoking pot has lost me.
In the end, as I know you've been told before, he is the only one who can make the choice. It's not like I didn't know my smoking was a problem for even the last 10 or so years, it's just that I was unwilling to do anything about it. Why? I don't know. My theripist asked me that question yesterday and while it seems so simple now that I'm clean, it wasn't at the time. Good luck and take care.