AW had a similar problem, not with people farming perks but people farming points. The way it was handled in AW was that if you shot down a pilot then you got full "points" for killing said pilot. If within a few minutes you kill the same pilot again, you received less than full points, kill the same pilot again a few minutes later and you get even less points to the point that if you repeatedly kill the same pilot again you'll end up getting 0 points for killing the player. A similar counter measure can be added to AH, so eventually the player ends up getting 0 perks for repeatedly vulching a 2nd account.
ack-ack