Easily done, lightly place your finger over the string (as when using harmonics to tune up 5th to 7th fret etc) pick the harmonic and dive the trem arm. There are some really high ones on the fret board up around the 17th and 19th frets. Easiest one to get is probably at the 9th fret. Try strumming the top two strings, then dive, you get a really interesting sound as both harmonics go out of tune. Satriani uses this technique a lot, so does Vai, Dime from Pantera used them on the end of "Cemetary Gates"... nice effect!
Experiment up and down the fretboard to findd which harmonic works best with what you are playing and practice the movement.
BTW another nice one is when you strum an open string (eg E), then as you dive it down lightly touch the 3 fret harmonic... sounds quite evil as the open note warps to the harmonic with the downward shift;-)