Just quickly,
Nettie have you tried (I'm sure you have!) putting the panadol in the side of his mouth?
I found when BJ was on Zantac (which he HATED) if we put the squirter in the corner of his mouth, over near the cheek, he swallowed out of reflex, but didnt taste anything

Not sure if you can do that with a "clefty" as I dont really know anything about that side of things

Might help...might not...just an option!