This sounds like the kind of contest where everyone wins. If you want to blow his mind, then just keep doing what you're doing. Don't premeditate anything. If he's as much of a "giver" as you are, then he's probably thinking the same thing you're thinking. Somewhere, in some alternate universe, he's submitting this same question to the site "Galspeak."
There really isn't any special position, or costume, or magical sexy word that will "blow his mind." I know magazines and "sexperts" would disagree. There is no strategy or preparation when it comes to sex. There is only raw spontaneity. Sex is teeth, flesh, spit, and curled fingers clawing. Making your lover have the kind of orgasm that will make his teeth light up like an old Lite Brite is easy -- just keep doing what you're doing. Keep playing the game of carnal brinkmanship you're already playing. It's sort of like dancing through a dandelion mine field. Don't stop swirling and dancing and laughing. Do cartwheels. Tumble with abandon. Eventually you'll set something off. Trigger a mine. But instead of a fatal ka-boom, it will be an explosion of moans and wetness.
This is the sort of question that isn't a problem.
@ Reformed Player > "There really isn't any special position, or costume, or magical sexy word ...."
Of course, there's a magical, sexy word......that us Latinas use.......ooh Papi yes! Si, Papi, Si!!!!! (oops, that's five words, but who's counting when you're giving and getting in return? LOL)