maybe do like for the "perfect circles". do a long running stitch (by hand) along the curve in the seam allowance and use that to gather it up and hold over the template, the press and starch heavily and press again until dry and set. If you need to, you can trim after pressing, or notch if you need to reduce the bulk.
Then pull the thread.
I also have an Omni-Arc square with curved lines for cutting circles, and it does work pretty well with my small rotary cutter (about 1" diameter blade). The smallest it has is for a 4" diameter circle, but I think the cutter would handle a smaller size.