Put it on and measure the gap where you can’t zip it up (A). Also measure with a tape from armpit (or side seam ) across your bust (B).
Carefully trim the zipper off but don’t cut the seam.
Split the last little bit of seam with a ripper and hand sew to match zipper area as much as possible.
Now take lots more measurements and mark up your project. You will need chalk or something to mark the fabric with. Lay the garment flat as if it was zipped up again.
Measure 1” from the edge and mark it (C). Do this to both sides. Next go along the area you just marked and mark the grommet holes, one per inch. Make matching marks on the other side and make very very small grommet holes on both sides.
Now measure and make a pattern for your insert. Move the top of the edges apart according to measurement A, that you took at the beginning and flatten the garment out so it maintains the same lines. Next with a big piece of paper (newspaper will do) layout out paper so it goes about a 1” over the grommet line. Mark this shape and cut it out of your paper.
With your insert fabric folded in half line up pattern you made with the folded edge of the fabric. Cut it out allowing enough edge for hemming/finishing. About a half of inch should do. Unless you want to leave it unfinished for a de-constructed look - then leave about a quarter inch. This will give you a ruched looking finish. I used a stretchy fabric as well as this is a poor man’s corset and the main piece doesn’t have a busk.
This is when you might want to finish all the edges on the insert or do your face stitching for the de-constucted look to stop fray and runners later on.
Time to open her up and add trim. Now use Measurement B from early on and cut out twice that amount of trim. This is gonna look like way to much but remember that the measurement B was when it was stretched out and you were wearing it and the doubled amount is for the extra ruffle. I am using the same fabric as the insert for a de-constructed small ruffle and so it is easy to install I am cutting the strip so that at least 1.5” will be under the edge of the bodice - I don’t want it bulky and scratchy . Next fold your trim in half and tack it to the center of your bust like so.
now using a needle and thread lightly tack in your ruffles to the facing of the garment keepin' in mind that the piece I am working with stretches when worn and so does my trim... so I am ruffling tighter than I want my end result to be. Also stop as you go and stretch the garment out and be sure you are getting the effect you want. You will sew it more securely a bit later in the project.
now sew in your panel. With the garment open pint the panel to the garment leaving plenty of room to clear the grommet holes and sew the strongest seam you can.
With the garment turned inside out repeat on the other side. The closing seam will be a pain the ass on your machine. Go Slow. Do what you have to by hand.
Now turn the garment right side out and cut tiny holes for your grommets through the panel you just installed. I am using stretchy fabric and I am worried about fray so I am going to “close the edges of the holes with a tiny amount of super glue before installing my grommets.
Now I am going to follow the instructions on the grommet kit to install them, but I am going to keep a thin towel between the area I am garmenting and the other side of the garment (so I don't’ cut the thing on accident.
Next install the lacing and try it on. Tying in the middle of the back. Adjust any of the paneling at this point as well as the ruffle detail. when it works to get in and out of easily measure the lacing and cut and trim. Then sew very very securely so it is one big loop stuck to the grommet like a proper corset. Then sew in your trim more securely. Voila! fancy bodice from 3 dollar thrift store find.