Watch the Double-Stop Jam online guitar lesson by Jeff McErlain from Essentials: Solo Electric Blues
As you may notice I am using my thumb over the top of the neck quite a bit in the tune. In fact, I use my thumb all the time on the low string. It really opens up left hand options such as adding in the sus4, 9, 11, and 13. I stole this from watching Jimi Hendrix, as I think many of us did! To really dig into this I recommend learning "Little Wing", "Wind Cries Mary" "Bold as Love" and "Castles Made of Sand" to really open up and see all that can be done using this technique. And what Jimi would do with it, it'll make its way into your playing just about as fast as you can learn those tunes!