Separate coutil strips are needed for the lacing on this corset since it's made with mesh instead of a heartier fabric. This same technique can be used if the fabric under the grommets is a contrasting fabric, and also when the center back doesn't run straight up and down but has a curve because of alterations to the pattern.
I've added along the center back below the waist to compensate for a hollow in the small of my back (This sounds more genteel than sway back, or the even yuckier sounding, lordosis.) so I started by tracing the center back pattern piece. I measured the width for boning and grommets, then added 1/2 inch seam allowance to each side (top of picture). I sewed the pieces together along the center back line and trimmed the seam allowance (middle), folded it over, and pressed (bottom).
After lining the sewn edge of the lacing strip-to-be along the center back I marked where the strip would be sewn to the mesh, flipped the fabric over so it was face-to-face, and pinned it in place along the seam line, measuring all the way to make sure it was exact.
The lacing strip was sewn to the corset, the seam allowance trimmed, and it was folded and pressed. I folded the raw edge in 3/8 inch and pressed. This will be on the interior of the corset and assures there is enough fabric to catch when the sewn from the exterior.
Everything was pressed in place, then from the front I stitched 1/16 away from seam, catching the folded edge on the inside of the corset.
I stitched 1/16 from the center back edge, then stitched channels for the boning.
Once those grommets are set I can lace up and do another try on!