If it's not alot of trouble (and if you have a scanner), i'd take the buttons and joystick out for one of the players, tape a sheet of white paper over the now empty holes, then take an exacto knife and cut out the holes where the buttons and joystick were. Then pull the paper off, put a sheet of black paper behind it, and scan it into the computer. That way you'd have a copy of the layout in the computer without
quite so much measuring. And, unless the layouts were different, you could reuse your scanned layout for the other 3 players.
You'd still have to measure to get the scanned image into place of course. If the controls are close enough to the edges of your CP though, you could use line the edge of the paper up with the edge of the CP. At least that way you'd have the vertical or horizontal position of the controls.
Definitely make sure to print a test layout to make sure it lines up.
I was about to do the same thing, except with just 2 players, 7 buttons each, but i decided on adding a 3" trackball, which lacks fitting between the player 1 and 2 controls by 3/8". Rather than shave plastic off of the controls around it to make it fit, and then measure the positions of all my buttons, to me it seemed easier to just make a new CP. But good luck in your endeavor!
