The best support is to "Keep your hands off the addict" because "this is his recovery".
It's our responsibility to work on ourselves so we are no longer a party to their addiction. No enabling. No controlling. No protecting them from the consequences of drug abuse.
Have you read "Getting Them Sober" by Toby Rice Drew? It makes some good suggestions about how to talk to someone in recovery.
Remember that he needs to do it for him. Your pride in his actions is not going to prevent a relapse tomorrow. Maybe just tell him: I love you. I'm glad you're clean today.