There's this part on the G3 Live video where he does something like that.

Yeah, I've tried the slap thing too (Steve Vai does it alot). There's another thing you can do with your palm. Fret a G major barre chord with your left hand, and place your right palm so it's barely touching the strings at the 15th fret. Strum it, and you'll get that nice "tinkly" sound.

Yeah, if you want to post a trick or mail me a sound file, that'd be cool.