That tickling compendium above by fingrfethr has just about secured the trophy for "Tickling Hell" as far as I'm concerned. If the boy is that ticklish I can't imagine that he'd realise anything else was happening to him if you added any of your normal "extras". I'd be off with the fairies anyhow.
But still, his tits are still free from torment so there's an opportunity and I wondered about raising the toothbrush slightly so it impacts the back of his nut sack, or even add another...