I was at the vet last Friday asking about this very problem. I'm happy to say his advise correspond to all the suggestions above - late night snack, smaller meals more often in the day,etc. He also suggested I add "Protexin Soluble", a multi-strain probiotic powder safe for use on animals, to all food and water as this aids control of scours (diarrhea) of non-specific dietary origin and helps to boost immunity. I'm going to try all these suggestions. Protexin Soluble is made in South Africa, so not sure if they export - contact for more info:
kyron@kyronlabs.co.za