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Sorry I missed this earlier

You could make some chew type things for him. My robo used to love egg box pyramids with seeds stuck to them. You cut one of the pointy inside bits out of a cardboard egg box, paint it with flour and water and roll it in small seeds. Then leave till dry. My robo was so excited and funny with his. He toppled it over, stuck his head in it and had quite a fight with it, but he loved it. Whimzees are the popular ones. You could try him with a Vitakraft honey and spelt chew also.
This is for a pack of 5 but you can probably buy them singly in a pet shop
Vitakraft honey and spelt chew sticks