resupply answer, maybe?
 

I take a rifleman and give all of his stuff to someone else, then load him up with all of a certain type of ammo that he can carry and basically make him a mule, then do it again with another one with different ammo, I use several of each, they then can interact with the gun or squad that you want.

The big limitation is mortar ammo, he can only carry 30 I think, everything else he can carry by the ton.