It seems like your post isn't getting a whole lot of response so I'd like to make a further comment. I'm interested because I've been there. I've read your post a couple times and believe your dog's eating problem isn't physical but he thinks you're trying to poison him with Vet food. He likes table scraps etc.. He's hungry.. If I can back up to our Rottie's eating, she can wolf down two cups of food in 50 timed seconds. She won't eat Vet dry or canned food. Have you smelled the food. The stuff I got smelled closer to drain cleaner than dog food. I have most of a bag left and we have coyotes through the yard occasionally so I'm going to see if they will eat it. If I find some dead yodel dogs in the yard I'll know why.
If I had your dog as a foster home, I would feed him twice a day. I would pressure cook skinless chicken quarters until meat & bones could be mashed by hand, about two hours, No chemical ingredients we can't pronounce. (I fry the skins until crispy, add salt, that is a treat for the wife & I. We wouldn't think of giving all that fat to the dogs. :)) That would replace poisonous commercial canned food. He would get 1/3 + - cup of this chicken mixed with a quality dry dog food. The morning meal would include a Sam-e pill wrapped in a small ball of raw burger or any other way to give a pill. The broth from cooking the chicken would be added to the dry food. (It is also used to make us a great batch of chicken soup.)
Anyway, God bless you. You are a rescuer.. But honestly, I think you're trying too hard. Your dog is trying to tell you. He ain't gonna eat that crapola.......... In my opinion... :)