Hypersmurf
Moderatarrrrh...
James McMurray said:... and nonlethal doesn't prompt massive damage save.
That could be argued

Of course, even if it's argued that 50 points of non-lethal damage from a sap could trigger a Fort-save-or-die Massive Damage check, it won't work on the troll, since:
An attack that can cause instant death only threatens the creature with death if it is delivered by weapons that deal it lethal damage.
But it does mean you need to be careful smacking the princess on the back of the head to take her back to daddy.
-Hyp.