Please see Double Stop Shop Parts 1, 2 & 3 lessons #'s 8572,8605, 8621 and Baby Blues Part 3 lesson #8271, which applies some of these double-stop concepts.
Here's a Groove Builder track good for practicing and applying what you learned in Double Stop Shop Parts 1,2 and 3.
It really should be an 8 bar groove, but I needed some chord changes on some beats I couldn't put changes on with Groove Builder, so I made it 16 bar, 2 changes per bar, and sped up the bpm. I also had to choose chords in a way which would "trick" the groove builder bass player to play the notes I wanted, so if you turn on the rhythm guitar be aware the results may not be what I intended.
The next page has some of my suggested double-stops to try over these changes, but please try and see what you come up with first.
You can hear how I've applied some very bent double-stops to blues in my take on add-a-tracks I posted here on my Rico's Gruv SoundClick page: