FIRST: Print as many "key_seats" as you need and put them aside.

SECONDLY: Print the "key_shell"s you've designed and LEAVE them on the plate! Add glue to the flat top of the key_seats and insert them into the key_shells ON the plate. Let dry, and remove once dried!

The key_seats should be printed in a slightly translucent filament to really let the LED shine through.

I've added an example "project file" with the ASWD keys. You can just copy them in the slicer and change the symbols for whatever you like. You can also decrease the font size and move them to a corner so that the "seat-post" won't block the light. It all depends on how small of a font size your printer can handle.

Let me know if you need help!