Unless you have the right equipment and by equipment I mean a cnc mill and and injection molding system and the experience to use it, this will not work. More importantly, there's no reason to, what you want already exists... Almost.
My advice,start with a backlit X230 or T530 keyboard, and adapt the backlight wiring.
The keyboard is pretty much the same, probably a direct swap (probably!) however I'm not sure if the motherboard has the proper connections for the backlight. Keep in mind, keyboard backlighting is going to match cpu and display power draw, if not exceed those. You're system at idle is probably 12 watts, the keyboard will suck down around 5 more. This was something people never gave the Thinklight enough credit for, since it only used one LED as opposed to 100. The Thinklight, also may be possible to adapt.
A better option, though more expensive, if you want to keep what you have, is buy a used T540 with backlight lower half. Your cpu, ram, screen, drives, etc... will all bolt right on. You will get backlighting, a better case, more ports... It's a small upgrade that gets you what you want in a bolt on fashion. Better yet, get a T540 base and cpu and install your parts, you can get a damaged T540 for $60, which is about what you will spend on the backlit keyboard alone.
