Oh, poor ds, I'm sitting at home with tonsilitus too and even as a grown up it is HORRID.
Top tip for future - go to a different chemist next time he needs ab's. We found one of our local ones favours vile pink clearish stuff that burns your fricking mouth off. Other one does either orange or banana, so much better.
With DD who is nearly 4 and just did 10 days of ab's 4 times a day for scarlet fever, i approached her knowing it was going to take possibly 10 mins of cajoling. I didn't shove the syringe up to her mouth as it freaked her out (are you using a syringe, I recommend as older kids can suck it out and if you stick it in far enough it hardly touches their taste buds.
Have strong juice drink in your hand ready plus choc treats. Tell him, if he does not take it, he will have to take even more medicine that is even more yucky (lie!).
If I'm very patient, and encourage her to put the syringe in her mouth herself, eventually she'll psych herself up to it.
After a few days, the become a bit fed up of making the fuss I find....hope you do too! Good luck.