Okay, followed the approach you described but seem to have hit into a couple more roadblocks. I tried both of these methods:
1: Use two arcs, make each circle using the Curve Loop node to meld them together. The problem I had with this is that my "circles" are generated with an XYZ grid -so that I have an array of circles, not just one, and the Curve Loop node is looking to stitch all of the curves into a single curve loop, not an array as I would like:
2. Use one arc for each circle, but have the arc be 360 degrees. I thought that the Create Extrusion Geometry node might accept this as a curve loop, but it didn't.