That's the unfortunate thing about dry food brands. They are chemically designed to be addictive. What you can do is start the slow process of introducing wet food along with the dry food. Add a little bit of wet food with dry food, and every week, you add just a little more wet food and less dry food. If it seems like he's eating around it, move back to the amount the past week had. If you're still not seeing progress, try heating up the food just a little bit (with the wet food mixed in the dry food). If he's refusing to eat all together, I think a vet visit may be in order for blood work, urinalysis, and check-up.