I don't have any practical advice for this. The only thing I know is that we can only do what we can do and after that, were helpless.
I'm trying to learn to let go at that point and trust my HP that what happens is what is best to happen even if in the short term it lookds awful. I'm also trying to learn how to do what I can calmly and leave the outcome to my HP.
I hope you are able to have peace in the fact that you are doing what you can and the rest is, after all, up to the addict.
And it sounds like he's doing all the right things and he has you. I'm guessing that the meetings and your encouragement are worth a lot. The accomplishment of holding on until he gets to rehab could be an important accomplishment to hold on to later when he is through treatment and back in the world.
God Bless - prayers that you find a resource at exactly the right time (whatever that is).