Kathy, my husband also had the amafostine injections prior to each radiation treatment. They always told him to drink water before the appointment, and take a pill for nausea. The medicine worked very well. He finished his treatments mid-November of 2002 and still has saliva. Well worth it!
He was given viscous lidocane (spelling?) which did help somewhat. Maybe there is something along that line that you could use right before you want to drink the Ensure.
Maybe you should consider a g-tube until your throat feels better. My husband was stubborn about that (still is) and lost over 70 lbs so far.
You can't heal if you don't get enough nutrition in you.
Hang in there.