Doesn't anyone here watch Seagal's movies? If you were that skilled you would kneel on the floor and tell the guy to "come and cut your heart out", then you would disarm him and mess him up real good, I don't remember how it goes exactly, I think then you would ask him if now he feels like a victim and then toss him into a couple of cabinets or through some glass
seriously though, unrealistic or not, I think the scenario Michael has described has more than two possibities. Why does it have to be either (trying to) kill the attacker or (trying to) "subdue him without harm". I'd take the knife away from him, and then subdue him, with a bit of physical harm, maybe break his wrist, his face, whatever. That'll get the point across. I mean people are talking about giving uncooperative ukes a hard time on the mat... I wouldn't even consider giving an armed (or unarmed for that matter) attacker on the street the benefit of the doubt.