Some dwarves are known to take isolate dining choices when given the option, dwarven personality and random choices actually come into play here. As long as a table/chair is unowned and pathable, someone will eventually eat there. If it's forbidden or owned for another use, they won't use it. I believe that if the table is inside another dwarf's bedroom, it won't be usable by any other dwarf. Consider adding a hallway behind the jail cells, with a bed. Remove the dividing walls between cells, so when you make that bed into a room, it encompasses every cell as well. Rebuild the walls - the rooms are now separated, but part of the same room designation. Assign this bedroom to any given dwarf, then seal the room.
The jail cells should now be inside a bedroom and unavailable to other dwarves (except that one). Making a prison cell from a chain should overlap the tables, making those tables "owned by this dwarf, but also shared and owned by this jail cell" and make them usable by that specific dwarf, as well as by the dwarf who's tied up in that cell.
For best results, make this 'dummy room' the actual room of your jailer. Now he'll randomly pop into a prisoner's cell and eat his delicious roast in front of the prisoners.
-This should work, in theory, never tested it myself. I just put my prisoners on the floor and throw strawberries at them.-