Last time i tryed this i was betrayed by my own gear ...
Not sure if this still works this way, since it was few patches back ... but in my case, i observed later that if you trully want to use non-lethal attack, you cannot give any damage on top of your basic weapon dice.
So if you have any item that gives you another +1d4 or +1d6 or w/e ...
Especialy elemental damage!
(I think it worked with Sneak Attack and Hunter's Mark ... maybe bcs its all the same type?)
They die.
I still dont understand why cant we change Race for our hirelings.

Lets us play Githyanki as racist as they trully are!