Satch's trademark harmonic dives

I have some idea of how to do these, but i still cant seem to get them right. Satch does them all the time (think of the last part of the solo in "circles")
from what i understand, it is just a pick harmonic on the open g string and then u whammy dive or whatever u feel like doing. i can usually do pick harmonics on fretted notes but i cant seem do do them on open strings.
anyone have thoughts on this?

[Evhmoon]

just pinch the open string with your pick and side of your thumb real quick in one motion.. kinda hard to explain..your basically hitting the string with the pick and very quickly hitting it with the side of your thumb a milli second later...which will cause the harmonic..just keep trying it over and over

[thefallenangel]

another one is to drop the bar and then pinch on the B and G strings open and pull up the bar.