Play any of the Key of G scales patterns over this D7 vamp. You can begin and/or end your phrases on the D note(Root) and A note(5th) for starters. This concept is essentially playing in the D Mixolydian mode.
This track features a Custom 7 string guitar made by Jimmy Foster. The track is a single take that has been processed to created two different sounds for the bass and treble strings. Here is a basic tab that you can view or download. This is a "six string tab" so I am not including the "D string" in this basic version. The tuning of the guitar is low to high - A E A D G B E.