The step kids aren't FF but I want them to eat better. We have pancakes every Sunday morning. It's a tradition. So instead of the maple syrup we have I emptied the bottle and put rice malt syrup in it. Master 7 said it tasted weird, Master 14 tasted it and said it must be the real maple syrup, not the fake stuff. Lol. Yep, the real one. Master's 11&11 both know the truth (one is FF, the other is half FF, of his own doing too) and I see them smile every time the other boys say something about the foods we now have.
As for the yogurt, get the proper yogurt and put loads of rice malt syrup and pureed fruit into it. Tell him this is what he is having now. If he really wants yogurt he will eat it. As his taste buds change reduce the sweetness.