I used 12 transparent rubber 'feet' which serve a dual purpose: they keep the board from flexing and they also prevent the plexi from getting scratched. Four black M3 screws are keeping the board in place.
The board is a good 3cm shorter and 3cm narrower compared to a board in the original case.
This is really cool. Did you need any specialized equipment or were you able to bend it pretty easily? I think I want to do something like this for my Poker or Leopold.