One more thing you might be able to do. I think I read somewhere that this sometimes has a positive effect.
Some people don’t realize how they behave when they’re drunk. They think, “I had a good time last night.” But what they don’t remember about last night is how drunk they really were or what they did. They don’t realize that they have a problem because they don’t know how drunk they get or how ridiculous they act. So if you videotape their awful behavior and show it to them when they’re sober, sometimes their reaction will be, “holy crap! All I remember was having a good time. I had no idea I turned into a slobbering, staggering, falling-down moron.”
As many here have said, it’s only when the alcoholic really decides to stop that there’s any chance he’ll stop. And sometimes they don’t decide to stop because they really don’t think there’s a problem. Occasionally, seeing that they get way drunker and stupider than they think they do will help them realize that they do have a problem and help them to decide to stop.