I saw MBI cork board last night and immediately thought it was a good idea. I had almost completed my purchase of them when I realised that the postage was going to be more than the item. So I left it in my cart for when I buy something else.
As an idle thought I fired up SW and tried to design one. I'm not sure that dimensions are totally accurate as I could only find the Imperial dimensions for the NEMA 17.
So, this is a work in progress. It will be updated once I have printed one and installed it.

(I take no responsiblity for any damage you might cause to your bot, self or small pets in the area.)

Remove pulley from stepper motor.
Remove 8mm screws from stepper motor.
Insert printable cork board onto motor.
Screw a nut onto a 16mm M3 bolt.
Use 4 of the above to secure the motor in place.
Replace pulley and adjust upwards 5 mm.