Holy Subdual( Book of Exalted Deeds, p. 44)
[Exalted, Fighter Bonus Feat]
You can turn bonus damage into nonlethal damage.
Subduing Strike (BoED) ,
When you use your weapon to deal nonlethal damage, you can also transform bonus damage from a holy weapon, your smite evil class ability, or your smite granted power into nonlethal damage.
A fighter may select Holy Subdual as one of his fighter bonus feats.