It isn't a "prohibition," we like GA frames too!
The grips on the GA are thicker, the same as the K series grips. The change Kahr made allowed them to narrow the grips but it took adding the boss to give the screw material to hold onto. If you grind the boss off, the screw will push right through the grip.
You might be able to find, or make, a wafer head type of screw, grind off the boss, and grind relief into the backside where you could epoxy in a washer to the back of the grip or something to give the screw something to tighten against. It would take checking that the head of the screw wouldn't be sticking up above the surface of the grip, hence the wafer head.