Litrely just did this the other day in my r33 gtst i cutout a square shape rounded the corners and used a fine file to bevel the edges used 2.5mm polished ally checka plate
did it with a hacksaw, file, ruler and a pen, piss easy (pen marks ally perfectly)
after u take the coin tray out u will notice it has a gradual slope so you can litrely jam the metal insert in and its firm as, wont fall out looks schmick
ive got some off cuts sitting around so if u want to send me out a envelope with $20 and ur adress i can make a replica of mine and 1 that covers the whole thing with 4 screw holes pre drilled so you can choose what one u want to run
pm me
p.s i also made another pannel to cover from my cd player to the bottom of the dash gap and cut a little square out so my gps mount sits behind it and my pen style turbo timer mount on it perfect