Ask him about lactulose, it works pretty fast. My old Badger used to get royally 'bunged up' on occasion and lactulose never failed. You use it just long enough to get things rolling. Not eating was never an issue
I keep a close eye on his ah, litterbox activities and if he is really struggling and his stools are very small, I add a 1/2 teaspoon of unflavoured Metamucil to his wet food, which generally takes care of the problem. When it doesn't (rarely) I use Lactulose.
Barium is constipating, so that may be holding things up.
PS The vet has to prescribe Lactulose, it isn't OTC.