Coup de grace

[MikelaC1]

Can a coup de grace be delivered so as to do non-lethal damage, i.e. KO an opponent?

[Morcleon]

Yes. You get an automatic crit (+sneak attack if you're using a sap) that deals nonlethal damage. However, by RAW, your target must still make the Fort save (DC 10+damage dealt) or die. A more reasonable houserule would be that they must make a Fort save (DC 10+damage dealt) or automatically drop unconscious, raising their nonlethal damage counter to that of their current HP.

[Beheld]

Can a coup de grace be delivered so as to do non-lethal damage, i.e. KO an opponent?

No. You can perform the coup de grace, but it will fail the save against death (that is not a death effect) and kill the opponent anyway.

[Necroticplague]

Yes. You get an automatic crit (+sneak attack if you're using a sap) that deals nonlethal damage. However, by RAW, your target must still make the Fort save (DC 10+damage dealt) or die. A more reasonable houserule would be that they must make a Fort save (DC 10+damage dealt) or automatically drop unconscious, raising their nonlethal damage counter to that of their current HP.

Actually, you're wrong about the risk of dying. It's squirreled away in an unusual spot, but it's written:

An attack that can cause instant death only threatens the creature with death if it is delivered by weapons that deal it lethal damage. So a nonlethal coup de grace is simply an automatic crit.

[Beheld]

Actually, you're wrong about the risk of dying. It's squirreled away in an unusual spot, but it's written:
So a nonlethal coup de grace is simply an automatic crit.

That's a statement in the Special Ability "Regeneration" if you don't have that special ability, that sentence doesn't apply to you. Just like the sentence "Damage dealt to the creature is treated as nonlethal damage, and the creature automatically cures itself of nonlethal damage at a fixed rate per round, as given in the creature’s entry."

[KillianHawkeye]

I'm pretty sure that a nonlethal coup-de-grace can only be done with a nonlethal weapon such as a sap, but it's too late at night for me to go looking for a rules quote.

[Morcleon]

I'm pretty sure that a nonlethal coup-de-grace can only be done with a nonlethal weapon such as a sap, but it's too late at night for me to go looking for a rules quote.

That's only for nonlethal sneak attacks. Nonlethal coup de grace can be done with any weapon capable of dealing nonlethal damage.

[Erit]

That's only for nonlethal sneak attacks. Nonlethal coup de grace can be done with any weapon capable of dealing nonlethal damage.

I.E. all of them. Even without bandying about the -4 penalty, just take Subduing Strike (BoED), problem pretty much solved.

[Morcleon]

I.E. all of them. Even without bandying about the -4 penalty, just take Subduing Strike (BoED), problem pretty much solved.

Yep. Unless a weapon is specifically stated to be unable to deal nonlethal damage, it can do a coup de grace since it hits automatically.