from Art Cohen -
Bow the open unmuted B and high E strings with a slide (brass works for me) near the 12th fret while muting the other strings. There's a certain sweet spot where both halves of the strings start to vibrate and an otherworldly high harmonic comes in. This even works on acoustic guitars!

Use the slide to bow the string or strings near the bridge while fretting. This works best using the neck pickup. On the low strings excellent growls can be created, while haunting out of tune melodies can be played on any strings. The strings can also be bowed lengthwise instead of transversely. A circular motion creates and interesting slow vibrato.

I play electronic space music on the guitar and have used the above techniques on my albums "Real Time" and "Available Space"