Good work. Make sure you use the minimum chocolate milk possible, so you can be sure he will drink it all.

If that doesn't work, I have had to resort to nose holding as well. It's very unpleasant, but it does work. You need to squirt just a little bit in at a time when you do it, and put the syringe down the side of their cheek and trickle it in - if you squirt it straight down the throat they may choke or vomit.