When I first started reading the topic, I also thought of ginger root.
If you put a piece of it, just a little bit, in the tip of his penis, it will burn a lot. But the good thing about ginger root is once it's removed, the burning immediately goes away and that gives you some control over the pain.
That wouldn't be the case while using icy hot or those other concoctions.
He would still feel the pain while masturbating but then removing the ginger root would alleviate it. It's a slightly different direction than what you were asking about, I know.
Good luck. Great topic!
Always,
Elisabeth