You know.... There used to be the option of join the army instead of jail. Admittedly for minor offences, but why not for major offences as well?
Issue a set of dog tags, a uniform, a parachute and whatever rifle the armourer figures they can most afford to lose.
Kick them out over ISIS run Syria and let THEM do the execution.
Seriously tho, I'm sure that outsourcing executions to somewhere like the Saudis or Indonesia would getthem done cheaply and efficiently.
The Indos popped the Bali Nine smugglers nice and neatly.