There is a cheat around that, though. I recently made a corset for myself on the spur of the moment. I used a newly drafted pattern with no mock-up, mostly to test my drafting skills. Overall the corset fit great, but the hips were too high and needed to be taken in. It was really distracting in appearance, so I decided to cheat fix it.
Here's a guide to how I did it. This is a really good option if you need to adjust the fit to a corset you've made this way after it's constructed. Hopefully you won't need it, because you'll have good mock-ups. But it's good to know it's an option.
Remove the bone from the seam and take the seam apart as much as you have to to fix your problem. In this case I used my seam ripper to separate the seam from the bottom up just past the waist.
Re-position the seam, taking in whatever you need to fix. In this case I'm taking some out of the entire hip, with the most taken out right beneath the waist. I cut a little off both pieces, and folded the top and bottom of the rearmost panel where I wanted the new seam to be. The panel in front of the seam slides between the exterior and the interior of the next panel.
Pin everything in place.
Step Four: Stitch the other side of your boning channel at the appropriate distance away from the first line of stitching (in this case 1/4")
|Interior of the corset|
Step Five: Reinsert your bone and that's it. The seam isn't as strong as it originally was because it's only held by two lines of stitching instead of three. And depending on your situation it may not be completely neat. In my case the inside seam doesn't perfectly line up.
And there's a new wrinkle on the rearmost panel. But since this was for myself and primarily for waist training, I decided it was good enough.