Drugs, chloroform, partial strangulation, a blow to the head? That’s got to be highly risky, unless you have a personal electric chair or lethal injection fetish. Even if it works, your mate won’t get much enjoyment out of it, other than watching the video.
Better to persuade him to act unconscious. It’s a real challenge for him not to react to whatever you do to him. His cock will give the game away, of course, and the contrast between his limp body and his stiffening erection will make the video more entertaining.
Hope you can share some pics?