I may have missed something answering this already but should I adapt the pattern for my swayback as I would for any dress pattern? Usually for a princess seamed backed dress, I subtract a full 1.5" block from the center back pieces at the waist (raising it) and re-add the length in the hip area. Then I dart the waist of the side pieces upwards, make a diagonal slash to then along the hipline and swing the lower area back to the original placement. The new "open" area generally equals the vertical s.a. length of the reconfigured center piece. Would this work for a corset? Or would this method be an epic fail considering the physics of a dress and a corset are vastly different?
First: I would ask you why you have a sway back? Sometimes it will be seen along side a bone disorder, such as scoliosis, when you may have no other choice but to make some allowances for it. Most often (and as the case with me) you see sway back as a result of weakened, overtaxed abdominal muscles, or too much weight being placed on the spine or abs. In this case I would not make the adjustment, but would add a few bones to the front and back panels of the corset and ATTEMPT to use the corset to correct the swayback on the person rather than in the garment. That is actually part of the reason I wear corsets, because they help to hold the bones in my lower back in place and alignment and alleviate pain resulting from swayback.