What type (brand/type) of food were you feeding your dog before he came down with this disorder? Has the vet done and ultra sound or X-Ray on your dog to see if he has gall stones? This is a very serious diagnosis. What type of food is he recommending that you feed your dog? Have you told your vet your dog won't eat the food he has prescribed? What did he say? You could try to mix in some canned drained green beans into the food to see if that sparks any interest, but check with your vet first. Green beans are pretty inert and shouldn't harm him.
You really shouldn't be giving your dog any treats at all when they are sick. This could be a painful condition for your dog and while th treats may taste good they may cause the condition to get worse. Just remember that a dog won't stave, he'll eventually eat the presciption food. I suspect that one of the reasons your dog isn't eating is because he's holding out for a treat. I've seen lots of dogs do that. Hold out on the treats and eventually he will eat his prescribed food.
And lastly is your dog overweight?
Sorry to have to ask you so many questions, but we have to see if we can find out what is causing the gall bladder to form this sludge in the first place. Also, has your dog been checed for heartworm disease and is he on a heartworm preventitive?