God forgive us, but there doesn't seem to be another end to this.
We should allow them to live in that same great state of euphoria that Terri Schiavo did. The autopsy said she didn't starve to death. She died of euphoria.
They may be summarily executed. While a trial is generally appropriate, it is not necessary for unlawful combatants whose status as such is obvious. As a practical matter a secret military tribunal holding a hearing which the prisoner(s) neither participate in or are aware of is probably appropriate. The issue determined at the hearing can and should be whether the prisoner(s) are more useful dead than alive. That would satisfy those portions of the Geneva Convention we signed, subject to exceptions noted by the Senate at the time, as opposed to the GC articles we didn't sign.
Then we should wait for an appropriate opportunity to execute them. It need not be a formal hanging. As an example of behavior modification, set it up so that one of them is provoked to do something he shouldn't while other prisoners are watching, such as throwing s*** or urine at a guard. Then shoot him on the spot, while the other prisoners watch. That would certainly have a deterrent effect on similar misconduct. They won't know that we've already decided to kill him.
Interrogation purposes - loudly tell the dude, in the presence of other prisoners, that this is his last chance to talk. Shoot him in front of the other prisoners when he doesn't talk. They won't know that we've already decided to kill him.
Or slit the throats of 5-6 of them, or whatever number is deemed effective, in front of another prisoner we're trying to impress. Some of these guys are really impressed by throat-slitting.
If one of them has a particular fear of drowning, or being eaten by sharks, take him on a boat ride with a bunch of these guys, tie them all up in chains with weights attached, do a phony random number means of determining who dies first but have your guy be last, or in the middle, demand that they talk and start throwing them overboard when they refuse. If your guy talks, he lives. If he doesn't, he walks the plank right there too.
Be cold-blooded about it. Once these guys are no longer useful alive, get some use from their executions. Use those to impress the ones you haven't decided to kill yet.