I think that sitting down with his family and organizing an intervention is a great idea. Have every family member, and yourself, and anyone else that cares enough about him to want him to seek help, write a letter to him about how they really feel, and how the are hurt by his behavior, alcoholism, and about how much they care about him and want him to get help and to get better. Then, organize a time and place where you know he'll go without too much fuss, his house maybe, and gather in a room with him, and read the letters out loud to him.

I've seen this done before on that TV show, Intervention, but don't know exactly how effective it is. I'm betting he'll either react one of two ways. He'll either say you're all out to get him and part of the "conspiracy", or just maybe, he'll realize that he needs help, as he's hurting the ones he loves as he is now.

I don't know if there is any chance you'd wind up on Dr. Phil, but taking a page from his book and trying to convince him that a disorder is as plausible as a conspiracy may be a good second choice. Though I'd give him some time and space between attempts, as to not overwhelm him and further delude him into thinking your out to get him.