Watch the Cabriolet online guitar lesson by Robbie Calvo from The Rhythm Architect
Given that we have a very full sounding 1st guitar part, I opted to create a 2nd guitar part that utilizes the open strings as a drone throughout the progression and is constructed from major and minor 3rds on the G and D strings. I did this primarily to keep the harmony simple and unobstructive. Play with this approach yourself as it can produce some really cool results that you may not always expect.
If you are interested there are also some really nice open string triple stop ideas that would work on this piece too. For more information on open string triple stops check out my TrueFire DVD 'Solo Craft'.