I hope this isn't who I'm thinking about but either way, if this person is a close friend, then I think you really need to be close with them throughout the recovery process. Of course they have to admit to the problem first but that's just one step. I think relapse will occur quite often if this person doesn't have a lot of close friends and support with them. So, if I were in your shoes, I'd either try to be there with them if they're close or at the least approach this person's other close friends and family where they live to try and help. They need to realize what this drug will ultimately do to them and you need to convince them there's much more to life than a quick fix. They need to appreciate the value of friends, family and what life has to offer without narcotics.
Best of luck to helping your friend Scott
WG