The only thing I can suggest is something I have done. The one cat that is a "grazer" and just wants a few bites and them to eat more later, just give him/her a small amount. I do this with Beep, even though the other two cats don't have access to her bowl, she is a grazer, so I just give her a smidge of food. Then I give her more meals, and trust me, she will let me know when she wants more. For us, it's not really a problem, because Beep can't be out when my other two are out. But my sister has this problem with her piglet kitten and her older cat, and what she does is when the older cat does not finish his food, she puts his food in the refrigerator for later. Then when he comes back, she will put him in a separate room away from the piglet kitten. Make sure the kitten is getting enough to eat, not sure how old but I'm sure you know, they do eat quite a lot of food when they are still growing.
Our piglet has to eat in the den, and just keep his little behind in there until my other boy cat and my dog....yes, he will try to eat food out of a dobermans bowl, he is that bold, so he stays in the den until everyone is done. Sometimes he is in there 30 minutes and thinks he's dying, but oh well. There is a litter box in there, he will not die.