I happen to like the cummerbund bettr than the satin vest, BUT....

If you don't wear the vest for anything else, you could put everything on and very carefully have the Goddess mark the bottom of the jacket on the vest. You'll want the vest an inch or so shorter than the jacket.

OK, when she marks it with chalk, and she'll have to be inventive with the bottom line of the ting in the front, then trim that puppy down. You'll lose the bottom button, for sure, and that will leave you with a three-button vest.

Replace the buttons on the vest with silver/pewter twins to the jacket buttons and try it again. It might work.

Then again, it might not and then you've spoilt a perfectly good vest.

Try this....no cummerbund, no belt. Hhowever make a small chain enclosure to hold the front of the jacket together. Basically this will be two buttons, twins of the ones you have on your jacket, joined by a -inch (roughly) length of matching chain. Orchard Supply Hardware sells shiny silver chain, it'll cost you less than a dollar.

Use the chain/buttons thing to limit how "wide" the front opening of the jacket goes, and wear it with NO cummerbund and NO vest. That's how a mess dress jacket usually works. if you decide to maket his your permanent solution then you'll want to replace one of the front buttons of the jacket with a button hole.

It's worth a try, anyway...try it before changing out the button for a buttonhole..