When firing an auto pistol the slide moves back to eject the current round and cycle a new one into the chamber. This is done with enough force to cause slide bite on the hand of someone holding the pistol wrong. However at the same time the slide of an auto-pistol can be held still without much force and prevented from moving.

In light of this, could the backwards motion of the slide of a pistol conceivably be used offensively in GURPS? If it could, how would this be modeled?

This is purely for style. A way to shoot one guy at a distance while knocking the one next to you up-side the head. Such a maneuver clearly offers no tactical advantage whatsoever and probably jams the gun, but it's cool as heck.