Have you tried Merrick? You add warm water and instant gravy. I gradually starting outting less water in their kibbles. That's how I introduce my kids to dry food. They eat raw morning and night and if they get hungry I have Innova out for them. By the end of the day the kibbles are gone. I did stop giving them treats too, until there plate was clean.
You are just gonna have to find a way to outsmart him, yes it will be a challenged.
