If he's willing to consider technology from my world while building it, he could make it programmable. Then, theoretically, anyone with enough comprehensive knowledge on how an object is constructed could program it to produce that object. It would... have to be something that inmates wouldn't have easy, unsupervised access to for obvious reasons.

[Being an inmate doesn't preclude someone from knowing how to program a weapon, for example.]

But even if it's only able to make simpler objects, it could certainly be useful! I'm thinking structural elements, casings, synthetic skins for prosthetics, that kind of thing!