If they have not committed any further crimes other than illegal entry, just push 'em across the U.S./Mexico border. If they have committed other crimes, take 'em to a point 3 miles offshore from Cancun, push 'em off the boat, and tell 'em to start swimming for shore.
The essential American soul is hard, isolate, stoic, and a killer. It has never yet melted. ~ D.H. Lawrence