Put him in a V18 tub or something similar in size and take him for a car ride
Car trip first and small enclosure second, the car trip does help I know it sound silly but I have used this trick to get some animals that had fasted for 6 months back on food after everything else had failed. Some breeders will actually ship out some non feeder animals to some other breeder friends to get them back on food as well (you just don't need to go to that extreme).
And of course the smaller enclosure just because cramped quarters are sometimes all they need.
Just some old breeder tricks you might want to give a shot to.![]()