How about pills instead of liquid. I'm presuming it's Clavamox, which can taste quite bitter. I use the pill form with my boy, it's still a stuggle, but unless he bites down on the pill, the bitter taste should be limited.
I wouldn't put it on his food, incase he associates the bad taste with his food and then you can have problems getting him to eat. You don't want fatty liver syndrome.
I don't think you can put anything in the liquid for flavouring, as Clavamox suspension has to be refridgerated once constituted and adding "flavours" might effect it's "Best before"
. Ask your vet though. If you can?, maybe chicken broth?