Ah, but we thought we were getting benefits from him – otherwise we would have expelled him from the country or imprisoned him, if we’d had any sense. So the analogy would be like if we later realized that the people weren’t cured at all, but we’d all acted as if they were. (And, of course, he hadn’t just laid on hands, he’d waterboarded the dying cancer patients).
That was explicitly ruled out in the OP.
I’ve got a question for the OP that I don’t think was addressed in the prompt.
Can he choose NOT to heal someone?
Example: Let’s say we have him in a cell where he is provided nutritious food and water (force-fed or tube-fed if necessary), but one of his hands is extended through a hole in one of the walls of the cell and locked into a restraining device, with the skin on the back of his hand exposed.
If you brought a patient to his hand every week (or month or w/e, depending on the severity of the cancer) and had them touch him, would they be healed? Or does he have the ability to suppress his power?
My thought is that the ability is entirely volitional on his part. Otherwise there’s no real dilemma; you’d just commute the death sentence to life imprisonment and then restrain/drug him whenever he had a customer.
OK, gotcha!
Yeah, it would have been a no-brainer but I thought I’d ask.
In that case I’d make him heal in exchange for food.
Edit: Scratch that. It was sort of an impulse response but I wouldn’t condone torture. Secure medical facility with weekly healings and research. Just like most of the other people answered. 
There’s (at least potential) value in keeping virtually anyone alive …
This. What we have here is an established supervillain who has promised that, in the future, he will use his powers for good, if only we won’t punish him for his past transgressions. I’ve read way too many comic books to fall for that old ploy! The faster we can yank the switch, the better I’ll feel.
I voted for the ‘dissection at a medical facility’ option. They probably won’t find anything, but there’s an outside chance at least of learning something useful. But leaving him alive is out of the question.
There was something similar during the run of the X-Files. Someone on death row can tell Scully facts on another serial killer but wants a pardon or his sentence commuted to life imprisonment. Scully takes the information, gets the serial killer and lets the other murderer go to the gas chamber.
I’ve got to start reading the OP before answering the poll.
I was the 63rd, “Move him to secure medical research facility. Weekly healings so he can be studied at work,” but I should have gone for my first impulse & been the 7th, “Move him from death row to maximum security. He’ll heal once a week in exchange for not being beaten.”
Either way, really.