It sounds a bit crazy, but I've looked up testimonials and people say it works.
I have no idea if a diet like the one you mentioned will make it harder for him, but it can't be good.
The good thing about Tsetsi's flush is that it doesn't seem to make people feel sick, but many people still flush out stones. I just started it today and it seems to be doing something, but no stones that I know of yet.