With Norwegian steeks, they don't add extra stitches. They secure two rows, one on each side of where they want to cut. I'm sure you could do the same with the sweater. Sew down each side of the center and across the bottom of where you want to cut, and hold your breath and go for it.
It will leave a jagged edge, but you could pick up stitches along it and finish it off so it looks neater.