Adam has a couple of really good Upper Octave videos on YouTube that really helped me. They kind of have the walking bass line start and build licks off of that.
When playing second position, don't forget that you can use any first position licks over the IV chord and they blend in just fine with the tune. So sample from Jimmy Reed's upper octave stuff and go nuts on the IV chord.
Same goes for third position licks over the V chord (but less opportunity to squeeze them in).
Last year, when I was obsessing about music theory, I wrote up a description of how this works, for myself. Not knowing any better, or what to call it, I came up with a name for this style of playing three different positions over the three chords. For second position on the I chord, I call it "playing second base". You can get my doc from box.net here.
BTW, the circle of fifths tells you what positions to play on the IV and V for any given position on the I chord.
