Could you tell them afterwards that it was just an experiment, that the experiment is over, that they showed admirable traits (if they did), and otherwise show kindness and care?
I think this would make a big difference to humans in an analogous situation. At the very least, it might feel more psychologically healthy for you.
It’s a great case, as long as you assume that AIs will never be beyond our control, and ignore the fact that humans have a metabolic minimum wage.