Warming food can help encourage to eat, theory is warm food smells stronger and therefore tastes more (try eating chocolate with a blocked nose, bland!). Dogs also equate moisture with palatability so I often add hot water to the food, then feed when it has cooled to a comfortable temperature. Easy enough to try very short term, and I couldn't agree more with earlier posts, don't wait for the preferred vet, this is a humane issue and the old boy deserves a little more. good luck.