Say you needed to lose 25lb and your husband laid down the rules. He demanded you exercised, eat healthy, no junk food in the house, etc. How well would that work for you if it was him forcing you, now multiply that by 1,000,000. Jmho.
Also, methadone or suboxone are very difficult to come off. I would do some research on Vivitrol now that you have come this far. But if he is not motivated to be clean, he will find a way. He may even switch his DOC if he is on a opiate antagonist.
I have to be honest, I, too, tried a very similar way as yours in the beginning, it had a disastrous outcome. I hadn't fond SR but I am not sure that would have helped. Like most, I believed my husband and situation were unique.