The "male" part of the winder mechanism is a hexagon with a threaded hole in the middle so it was pretty easy for me to make something that would fit. if your car has finer splines it might be a bit more difficult.
Step 1: Plans
then find a design you like, could be anything but i went with simple chevron cutouts. make a line drawing in a 2d software - i used illustrator, but check with the laser cutters to see what file format they can use.
looking at the drawing below, starting from the bottom up:
1 - Back plate with 3 threaded holes
2 - base plate, 4 holes. the hole will need to be beveled so the head of the screw doesnt stick out.
3 - handle
4 - spacer
Screws will go through the handle and the base plate, and thread into the back plate. the middle hole in the base plate will hold the entire winder to the mechanism. the idea was to have a minimal amount of screw heads visible, so being able to hide the middle one meant using a baseplate. this makes the assembly a bit tricky but i think its worth it in the end.
Measure everything again just to be sure. Now you're ready to get it laser cut!