Do you feed him first thing in the morning (after he goes potty of course)? Vomiting yellow stuff is 99% of the time just a sign of an empty tummy. When I was working out Alice's pickyness, she was only eating a few bites in the morning and if she didn't eat more, after an hour or two she would do the same thing. Our Akita will throw up yellow bile too if one of her meals is late for some reason (if we sleep in on a weekend or get home late to give dinner).
I'm not using TOTW, but I do know what you're talking about. Try making sure he eats well right away in the morning and that should do the trick
