Thanks for the suggestion @MikeTO. I tried 2 strokes with different offsets (outer and inner), but could not separate them or achieve what I need. Perhaps I didn't describe what I'm trying to do clearly.
I'm trying to use the line (eg. pen, shape outline via thick stroke) feature to create shapes that are mostly just symmetrical outlines so many points/pixels in width. But sometimes I want to pinch or stretch just one side of the thick line to achieve a specific shape.
Say I went to make a 'speech bubble' from a circle outline. I might start with this:
But now I want to pinch the curve into a sharp point. But since the outline is a single curve, not two, I don't have control over both edges.