Hi scott_b. I'll have a go at this asap, but I can tell you that the
PT mindset would be to play around with the chord tones. I hear a super extended A7 myself, meaning that I would look for lines in amongst the 1-b3-3-5-b7-9-11-13 -- and of course the underlying chromatic -- in other words just about every note going.
So let's first hear something you've recorded over this and give us an idea of your mindset, since you're asking the question. I've always found one-chord-vamps a little boring to play to ... melody loves chord tones, especially when there are at least a few going on. As you point out, one chord-vamps are not easy to keep interesting.