Honestly, I think adding anything is risky b/c they could become spoiled. I have a picky eater and soaking his food seem to help, but he 10 and doesn't have the healthiest teeth. When I add things to his food, he eats the treat and leaves or even spits out the kibble. I would try giving him the food and picking it up after 10 or 15 minutes. Make sure you do it several times a day, so he doesn't become hypoglycemic.