one of my old singer sewing books shows doing just about the same thing - but with a regular machine, darning foot and feed dog cover plate. From the time when clothing was still too expensive to toss out. The key is to keep the moving so you are pulling the thread across the open area as you stitch, but no different than free motion quilting.
Once you build up the netting to fill the gap, it gets easier and you just keep going over it until you've built the thread layers up.
I do love that machine! Having the rolling bar would make it very easy to do. I also don't think dealing with a curve is that big of a deal, and if you really don't want to deal with it, then undo the seam enough so you are dealing with a flat area. Though you may need to baste some waste fabric to the edge if you are going to be sewing close or on it.
My time spent in the alterations shop comes in handy - mended and altered a lot of stuff during that time.