I've always had this thing for being forced into being female. Of course when you enjoy it, it's not much of a "forced", so fantasies drift into transforming other males into being a girl, especially those that truly are forced who don't enjoy it. The first thing that comes to mind is "tie him up, hold him down, perhaps drug him to pass out". Those are all cliche' typical storyline approaches. One alternate that I've thought about as long as I can remember is hypnosis. Taking someone's inhibitions away, perhaps taking away their realization that your even transforming them. While in hypnosis, many simply have no control (within reason). You can have them sleep, and they won't awaken until told to do so.
You can freeze them in place, even force them to have an orgasm:
Even better yet, hypnotize them into believing they're actually a woman, and have them dress themselves
Or perhaps even have them put on their own makeup