Yeah, I've done it. Not fun, but the results justify the effort.
Go to your local Wal-Mart. Head for the craft section. Look for a bottle with a yellow label marked "The Scrapper's Solution". This is the jumbo-economy-sized container of the product called UN-DO, aka heptane. $5 will get you a full four ounces. The same thing sells in most hardware stores without the scrappers moniker at $5 for one ounce.
Find a well ventilated area to work and a six inch thin metal scale. Working with the back off of the calculator, apply the UN-DO to one edge of the metal label. Keep it wet with UN_DO for about thirty seconds for the solvent to work. Slide the scale under the plate and work it free. Where the UN-DO soaks in, the adhesive lets go. You work your way under the entire plate, slide the scale under the plate and applying more UN-DO. It will take at least ten minutes to free the plate from the calculator back as the acrylic adhesive has a death grip on both sides. Don't deform the plate any worse than it already is, this is the artsy part of the equation.
Great gooey, sticky fun with noxious vapors to add to the enjoyment of the moment.
Once off, remove the adhesive from the back of the calculator using denatured alcohol. The black carrier film will probably be left on the metal plate. Peel it off and then remove the residual adhesive.
Now comes the fun part. Find yourself a really good rolling pin and flat, hard surface. I have a marble rolling pin and board used for making pasta. It works well. Just roll the plate flat. Press too hard and it curls. Flip it over, roll it again, bend to suite, warp to fit, etc, etc. Just knock yourself out until your happy with the flatness.
Get some double sided carpet tape, peel one side and cover the back. Trim it 1/16" from the edges. Cut out the two spots where the ESD springs from the front make contact with the back. Peel off the other protective film, line it up, press it down and enjoy.