I have not printed this thing yet and I don't know if the measurments are correct - especially for the t-slot that should fit on the switch. This is my first try, but if you find it useful, be my guest - use it.

Update: I redesigned the key so it will be more likely to fit on the switches. I remeasured and found that the base of the switches is 15mm square, while the hole in the older design was only 12mm square. I hope this new version will work - but I still haven't tried it.

Update2: I cleaned up the new version so it has fewer angles and the bottom is flush - just a bit of cosmetic work. I set the bottom view of the cleaned up version as the new default pic.
Also sorry I didn't mark this as a work in progress, because I didn't realize how much I would modify it when I first uploaded the original design... But I guess I'm happy with it now, so, I hope this was the last update - unless I should find out something doesn't work out once I printed it...
The "print ready" version of the .stl is turned 180° so it should be printable without supports...
I also made a version with thicker walls for the central peg (Key print ready strong.stl -if you couldn't tell yourself) - the older design looked like it might be difficult to print...


Ok, I made one and, as was to be expected, there were some issues:
I printed the "strong" version with the thicker central peg, which was a good idea, because even the strengthened peg ended up with rather thin walls. The x-slot did not print properly - I lost about 0.5mm in each direction. I revisited my files and tried to compensate for that in my newest version. We shall see in a week how that works out.
Beside that I am very pleased with how it turned out. Using a fine file I was able to widen the x-slot enough to make it fit the switches and the overall shape came out as I hoped it would.