That's what I wound up doing. I'll go into it more with the next sewalong article, but I marked the casings with masking tape on the outside of the corset, basted along one edge, took the tape off, turned it over and basted the casings in to the inside, turned it back over and stitched the casing from the outside using the basting line as a guide. Then I used the first stitching as a guide for the second set of stitching, put that in, and picked out the basting. It's definitely not perfect inside, but it let me pay much more attention to the way the top stitching looked on the outside.