Where there is a will, there's a way. If he wanted it bad enough HE would seek it out.
Has the rehab given him ideas, other options? I'd be surprised if they didn't. Did he come home with a treatment plan? This is usually what one leaves the hospital with. Although I know he was planning on going back, there still should have been a plan.
Callie let him seek this stuff out himself, or leave. It's not your job to be his treatment manager. If he doesn't do it, he doesn't want it that bad, period.