That sort of seems like a..lot for Blanque to be able to do from in a cell. His area of mental manipulation seems to be fairly short. His only two showings of mental manipulation have happened from within the Fortress he was trapped in. I actually think Blanque is being freed just to set him up as a foe for later.
Edit: Also he never "jailed" Henshaw. Hank was unconscious from the crash, strapped to a monitor to check for anomalies, controlled by Blanque, saved Superman, then was dropped of and free to go. He was put under medical care and monitoring.