Although it would require a little more work and an additional addon, you could D/L one of the many invisible target addons and then use one of the armour ones to createvehicle it then setpos to one of the infantry units. Just a concept as I have not (yet) tried it myself.
Wadmann
This absolutely works. I've done it. I'm using invisible targets for:
1. Get choppers to use rockets on ground infantry.
2. Get AT soldiers to use AT on ground infantry or fixed positions where infantry dug in.
3. Get infantry units to fire on armored units (I love the MM-1 grenade launcher opening up on a BMP until it takes enuf damage to eject its crew!).
I haven't tried attaching an infantry target to a chopper yet, but think it will work (i.e., get ground infantry to finre on chopper).