Pinning Knockout
An opponent you have pinned is easy for you to knock out.
Prerequisite: Dex 13, Greater Grapple, Improved Grapple, Improved Unarmed Strike, base attack bonus +9 or monk level 9th.
Benefit: While you have an opponent pinned, when you succeed at a grapple combat maneuver check to deal an opponent nonlethal damage using an unarmed strike or a light or one-handed weapon, double your damage result. Any creature that is immune to critical hits is immune to the effects of this feat.
Source: Ultimate Combat, p. 113