There's also another way that thumb pick-players use. This technique also works without any kind of pick. First you find the harmonic by holding the side of your RH thumb right over where the appropriate harmonic is, and then you pick it with your index finger. Once you have found the harmonic, you pick with both your thumb and your index finger at the same time. Thumb going down and index finger going up! This will give you the pinch harmonics.

Brent Mason explains this technique in his Hotlicks video. You can hear the start of his explanation as well as a demonstration on this link. It cuts off unfortunately, but it get's the point across....

http://www.youtube.com/watch?v=Pcq89Nj-1RE

Anders