You know, I was being my sarcastic self but I think you are on to something. Send in mercenaries and what they take, they keep. That would work.
...And the Cartel's paid politicians would claim the US is paying the mercenaries to invade the soveriegn territory of Mexico, which brings in the Federales, and of course the UN would have to get involved...
Meanwhile, our own BATF is STILL walking guns to the Cartels, which are killing US citizens who were hired by expat Mexicans to clean up their country...
Who writes this stuff anyway?