Well, let me just tell you, it did not beat me. I DID prevail!
This vest was pretty big on me, so much that I could see that fitting it would mean removing that entire middle panel of the back. So that is exactly what I did, and used the shaping lines as a guide and extended up from there.
I left a large seam allowance when I cut the back knowing that I would need that to be able to reconnect everything with all the seams still covered inside the lining.
Now this vest is lined with the self same fabric meaning that there is no need to finish the edges since they are all hidden by the lining. I unstitched the bottom edge so I could access the separate layers.
I planned to sew it right up that shaping line, so I had to clip off the ties.
To reconnect everything, I worked with only one layer of the vest first. Then I flipped it in on itself and sewed the other layer, leaving an opening in the bottom so that I could pull the fabric from inside.
The shaping lines ended up being part of the design on the back of the vest, like a v right in the middle. Looks kind of neat huh? And I thought a T back made it interesting.
Now I said that I had some trouble....basically I had to keep adjusting the back so that it would lay nicely. No point in showing all that resewing, trying it on, resewing, trying it on, etc. Suffice it to say, I finally got a nice flat fit, and then top stitched the armholes on the back so that they looked finished and not so puffy.