Hey Jock Briton, like Pickled Lemons said, we would like more details before rendering an opinion. We want you to be as successful as possible and, as everyone is different, we need more details.
In a general sense, I think this is a pretty sound way to go. There is a lot of variability among detox centers. Some strictly use Bupe to detox, which I'm sure you dont want.
I think you should get your Codeine level down as far as you can before detox, then utilize the comfort medications they give you to help you make it through withdrawa without too much trauma.
Good luck! We really would love to hear back from you about how things went. You can do it buddy.