Like David, the antiemetics didn't work all that great for me either and I didn't even have Amofostine. I ended up using Compazine suppositories because I couldn't keep anything down. Some people are just sick a lot and it's very hard to watch as a caregiver. Keep on the doctors about managing the nausea and stay on top of being well hydrated (2-3 liters/day). Vomiting dehydrates you very quickly and that will just make things worse -he might end up in the hospital ER for rehydration (make an appointment in the infusion unit if you can - it's much faster and more comfortable than the ER). I vomited so much that I actually polished my teeth like glass from the stomach acid. Speaking of which, Cisplatin is tough on the stomach lining so antiacids are commonly prescribed as well.

If he's PEG feeding use a slow drip method and see if that helps.