I use 6mm Acrylic squares and some hot glue. 1u = .75 x .75". To completely fill the space between PCB-mount switches, I use .875 x .875". Those cost me $1.00 each (minimum piece cost) at TAP Plastics.
But I've always wanted some blockers that would fit into PCB and plate-mount holes to replace the missing switch
and fill the space above. So I launched CAD and created 1u and 2u designs, then uploaded them to Shapeways to get prices for 3D printing in a variety of colors.
MX Switch Blockers in 1u and 2u sizes by samwisekoi 2014The 1u would be $3.60-4.75, depending on color and finish. The 2u would be $5.10 - 6.10. These are solid; making them hollow doesn't change the price enough to make it worthwhile.
I am happy to make them available on Shapeways and/or provide the design file to people with 3D printers.
- Ron | samwisekoi