I guess the key is knowing which rehab he is going to and contacting them for their requirements. Detox is usually quite short. Has he indicated what he is willing to do?
You are right you can't force him. However, you can state what you are willing to do or not do? For instance, as can say anything you like. It's your life and your home still. If you tell him that he is welcome to stay at your house, sober, until he is in a rehab or sober living or whatever. Or you can give him a time frame of how long he can stay with your. It's up to you.
Boundaries are VERY important when an addict is in the picture. Mean what you say! Writing out, on paper, is helpful to get your plan together.
He may not choose the option that you hope and pray for....it has to be up to him.
Again, the detox place should have information. Has he mentioned anything regarding after detox?