K.H.
My son had the same thing at that age - I felt so bad for him! My Ped. (Who I love) told us to give him tiny sips of Pedialyte mixed with flat coke - you can add ice too. The trick is that you give him sips about every 10 minutes and just a few. We actually had to set the kitchen timer. It was time consuming, but so was cleaning up the vomit if he had too much liquid at once (: We also gave him the good old "BRAT" diet for upset tummies (Bananas, rice, applesauce and toast). We couldn't get him to eat so we gave him Pedialyte over ice chips which also keeps them hydrated, but slows down the intake of fluids so they can digest them.
The main trick is to keep him hydrated as well as keeping him from vomiting and spacing the liquid does wonders. It last about 2 and a half days of vomiting and a week of not really eating.