Jimlock
Adventurer
For me, the problem with the rule is that the player controls whether the damage is nonlethal or lethal. This should be determined by some other method because, in real life, it's hard to control whether you beat someone to death or just beat them unconscious (and that unconscious person is likely to have some real damage to him like broken bones and internal injuries).
I believe that a way to figure this out would be nothing less than "pretty complicated".
I might sound boring, for I use this same argument time and again in your threads, but:
The game is already complicated as it is.
To resolve something like that "realistically",
would normally involve another dice roll or some accounting based on the dice already rolled,
so as to figure out whether a hit deals lethal or nonlethal damage.
Even if you find a way to do that, you would not get the desirable result.
The hit-point system is so vague as it is...
...and made like that, so as to resolve damage in the most general of terms.
Personally, I do not see a way of getting what you want,
without some complicated changes in the combat system in general.