This is a difficult one. I can see why you are so concerned about your friend.
The alcohol, while it does dull the pain, also aggrivates the nerves that are involved in RSD/CRPS. You are correct in that certain meds are off limits to him if he has an alcohol problem (they can be deadly.) Pain Management Docs can diagnose and do nerve blocks which can be helpful in the very early stages of RSD/CRPS. This would of course be a doctors call, but he might could get those even w/ the alcohol problem. Most pain docs will drug screen, so it will help his treatment in all ways to be honest about the alcohol.
Second, if he is willing, he very much needs a pain management/substance abuse counselor. If he is willing is key there.
It seems to me that proper diagnosis and looking at treatment options, both for RSD/CRPS and the alcohol problem, are the first line treatment options here. You are a good friend to sitck by him. I hope this will be of help in some way~mama mac