How to feed hopper when owned by prisoners?

How do you feed a hopper in a prisoner area, for example for a nutrient paste dispenser? When I try to direct a colonist to feed one, I see the error "Cannot feed hopper: reserved for prisoners."

Hoppers are used by Nutrient Paste Dispensers to provide food for turning into paste. The hopper needs to be next to the dispenser to feed it, but hoppers can't be in prisoner areas because colonists won't fill them.

But... dispensers are pretty big, so you can construct one into the wall of your prison, such that the front is accessible by prisoners, and the rear is in a non-prisoner area, into which you can put your hoppers. Colonists will happily fill those hoppers as they're not part of a prison.

Below image taken from this answer to a similar question (which is a good read if you're looking at mass prisoner feeding solutions.)