Why not just introduce a new combat declaration in addition to Precise Attack, Bypass Armour, Disarm, Location Strike and Strike Weapon/Shield.
So, you could have:
Non-Lethal Attack
A character making a Non-Lethal Attack makes a careful attack designed to stun rather than permanently damage his opponent. Attack, reactions and damage is rolled normally and applied, but the damage is only temporary and lasts until the damaged person makes a Resilience Roll. Damage caused by a Non-Lethal Attack counts towards location damage as normal and can knock a person out, render a limb or vital location useless or disable an opponent.
Non-Lethal Attacks are like normal attacks in that they can cause critical hits and be parried or dodged as normal.
Non-Lethal Attacks may not be made as part of a charge or flurry. All Non-Lethal Attacks are very difficult, the character's Weapon Skill suffers a -40% penalty. Non-Lethal Attacks cannot be combined in a single strike.