Like this. I put the ruler down to show that's where you draw the line, then you just sew a wavy line around the line. I drew lines 3" apart on this and did it in both directions. What's nice about this is that you don't have to be perfect and because you're not dropping the feed dogs, you don't have to worry about your stitches on the backside. You do need to use a walking foot, though.
that looks and sounds like a great plan!