You needn't apologize, MANVIN, really. The problem is much more complicated than what I had understood, and, well, I like that !
I'd say something can be done with the "nearestobject" command, and "addeventhandler", but then variables would depend on the specific number of choppers of some kind you're using, so actually I think more info is needed, here (at least that's the way I see things, hopefully someone might come up with a simpler way).
But I also think that you want to do something complicated, whereas there can be easy work-arounds : if you pre-assign each unit to a chopper, taking the number of cargo into account, the problem looks solved to me, regardless of all the confusion that this might create...
Anyway, my brains are overheating right now... Good luck, then !