It is frustrating, however, it is his doing, not the rehabs or yours. It does sound like the logistics are a nightmare, however, many people have to negotiate through those things in life, and learn to deal with them a step at a time. It sounds to me as though he toes the line just enough so that you won't kick him out.
My heart hurts for you as I cannot imagine. In no way am I being critical or judgemental as the fear of losing your child has to be overwhelming.
I think you have to do what you feel comfortable doing yourself. Maybe that means him getting clean in inpatient, having requirements, one being a job after so long. He has to grow up, learn responsibility, and want this, badly. Those are responsible adult things that he has to strive for to be a good citizen and kick this.
I send my prayers to both you and your son.