Watch the Nastophonics online guitar lesson by Jennifer Batten from Rock Sauce For Lead Guitar
Start with some distortion for this. The more you have, the easier it is to get the harmonics to pop out. When I do this, I find my right hand index fingernail ends up with grey coloring from the strings, so obviously my fingernail is involved in getting the sound. It's a combination of using the picking fingernail and using extra pressure in the right hand. I also change the position of the pick in my right hand and grip down closer to the tip than usual. It's a technique that takes some experimenting.