Yes the mouth has really healed up well. When we got him, his gums were bleeding and very red. Now his mouth is a nice whitey-pink colour. As far as we can tell his mouth is free of ulcers now. When we had him to the vet last week, she was very surprised at how good a shape his mouth was.
We have tried just about everything we can think of with the food. Haven't tried the catnip on the food and we know he likes it because it's on one of the scratchy things our cats use all the time.
We've tried nutritional yeast - we've used it before with our other cats - but it didn't work. The food is always warm when we give it to our cats.
Human food of any sort doesn't pull his trigger at all.
I've put butter on capsules when administering vitamins and he's not impressed with that, but haven't tried melted butter on the food.
Thank you for the suggestion and we'll give them a try.
One of these days, this cat has to start to eat something on his own.
Any other ideas graciously accepted.