Supporting and not Enabling

My son is a heavy marijuana addict. He smokes all day long. He is not employed and he has no interest in changing. For personal reasons I do not want to ask him to leave though at 26 he is a legal adult. He is not diagnosed but he is definitely struggling with mental health issues on top of his addictions. He will not see another counselor. At this moment in his life I just want to keep the peace in the house as much as I can and try to help him move in the right direction and also help him with a harm reduction approach. He is basically ambivalent about cutting down his marijuana smoking. He agrees that he smokes more than he should but he is not willing to do anything serious to try to cut down (like see a counselor or go to NA meetings (He has been to these before and he did not care for them). I would like to help him cut down but I can’t come across as threatening or he will rebel against my wishes. Can you advise me on some baby steps I can use to get him to gradually move in the direction of cutting down?