Take the seed away. It sounds mean, so get a scale to keep track of his weight. We never feed any seed at all here. I get lots of seed eaters here, and as long as they still have access to seed they often (not always) decide they prefer seed. Like setting broccoli and chocolate cake in front of and eight year old.... most of them will eat the cake. Nutritionally same situation for parrots seed = chocolate cake (very tiny amount should ever be offered). Some birds get something akin to seed addiction, and can be quite tough to break them of it. Of the 40 birds I have here, every last one came to me on a seed diet, and not a single one eats seed now. Monitor his weight, and ask a vet about the safe weight range (so you know when to be worried), offer a couple types of pellets, and a full variety of fresh foods (chick peas/ garbonzo beans are well received by most birds). Frozen peas (thawed of course), and whole wheat pasta, and sweet corn are all the normal favorites. Green beans, broccoli, greens, kale, bok choy, tofu, squash, green apple, carrot, and sweet potato are a little tougher and take longer to transition them to. There is a Yahoo group called feedingfeathers that can answer a lot of specifics, and can provide some excellent well accepted mash recipes, along with explaining when and where seed is appropriate in a psitticines diet. Good luck!