I sometimes have trouble swallowing pills too. When my anxiety is bad, my throat becomes very tight and I have trouble swallowing, feel like gagging, etc. Peppermint confuses the gag reflex, so what works best for me is taking my medication with tepid peppermint tea. It might be hard to get your son to drink peppermint tea, though. I love it, but I know not everyone does.

If I need to take a pill when I'm out or at the office and don't have peppermint tea, I eat a strong peppermint (like an Altoid) right before I take my pill. Having that flavour in my mouth seems to keep my gag reflex from kicking in when I'm swallowing the pill.