Bret! I agree that you are a great friend for trying to help - it's not easy.
I was on pills for about 2 years and struggled with trying to get clean for about a year. I now have 3 months clean. I'm a little younger at 23 but it sounds like we grew up experimenting in a very similar manner.
I had legal motivation (drug court) to get clean and I still had trouble. I actually complete the program tomorrow but I plan to stay clean because things are going wonderfully. If he doesn't have the motivation to quit it's going to be almost impossible to get him to quit.
Anyways, pot will help with withdrawals a little bit but I am willing to bet it will not keep him clean. Suboxone is a great drug, I am on it. I've been taking it for a year (I would stop when I relapsed because it is an opiate blocker) and I am now down to 2mg a day. I think Suboxone will be the best thing to get him on. Some doctors don't really understand it yet because it's fairly new and they will prescribe A LOT. But I cannot give ANY medical advice because that is against the rules here.
Really, I'd recommend him quitting everything - drinking, pot, pills, etc because cross-addiction was a problem for me. I'd quit pills and start drinking like a liter of liquor throughout the night or smoke a bunch of pot or whatever. I think a lot of people will agree with me on this topic - that quitting everything is the only "real" way to recover.
If you'd like you can email or chat and we can discuss this further. I have google chat and aim which I'm not on very often but I'd sign in if you want to set up a time. I'd like to help as much as I can but I don't want to break the rules here.
email - allennyberg (at) *****.com
aim sn - fluxriffs