I'm not close to mastering it but I wanted to post a video because I know my parents read my blog and will think this (and by proxy, me) is cool! Here is all 12 seconds:
To play squealies, you press on the whammy bar to loosen the strings (which lowers the pitch), flick the G string with your left/fretting hand (or any string, but G sounds the best), and immediately add a harmonic (again with the left/fretting hand) while pulling back on the whammy bar to tighten the strings (and raise the pitch).
In the video I play three squeals on the G string with harmonics on the fifth, fourth and third frets. I'm just using my crappy practice amp on low volume and my laptop mic with no effects, so it's not as deadly as I'd like... but the potential for deadliness is there!