I don't know if you tried this already, but perhaps a vet formula food for sensitive stomach would help. It's almost the same price as the premium pet store foods. Or cooked chicken with rice if he eats it. I know I read here a post about not feeding our kitties tuna all the time because of the heavy metal content- but I do understand you want to have him eat something right now.
Our Heidi who is highly stress-able vomits flegm when her stomach is empty, mostly in the early morning. Stress can do weird things to the body. Good luck to you, poor little guy can't be comfortable throwing up so often!!!
Marina