This modification is not that difficult. All you need to do is to find a 1994 or 1995 Thunderbird or Cougar with a locking gas cap. A typical schematic is as follows:
Go to the junk yard and remove the gas door and keep the hardware. Then open the trunk and remove the solenoid valve (and hardware), pull level and the wiring going behind the bumper up to just behind the seat. Then open the console and remove the button and wiring harness as far as you can get it.
Installation is the reverse. The bracket for the solenoid and location for the console button punch-out are available. Install the power to the ignition on switch so no one can open the cap with the key off (unless they have trunk access). When installing the door be careful not to double up on the washers. Otherwise the door will not be smooth.
Here is a picture of the door just after installation.
I painted the whole car afterwards so I did not worry about color matching.
Here is a picture of the console with the yellow door open switch.
Works like a champ and looks stock!