Maybe I'm a little slow on the topic, but why not just make a sabot rifled slug with an AP core for the 12 gauge?
My father (admittedly a consummate marksman) has taken whitetails with a 12 gauge to 200 yards. I would think the ranges involved for disabling vehicles could be comparable to those of this rifle/ammo, and the ammo could be used across a range of platforms currently deployed with LEOs and Military alike.