This modifies the back right foot to hold a combination C14 socket and switch. You will need to use a M3x12mm screw instead of the M3x16 called for by the original build.

This is similar to the combination socket and switch I purchased:
https://www.google.com/search?channel=fenc&client=firefox-b-1-d&q=c14+fused+plug

The fit is pretty tight, so the screws aren't super necessary. This also means that you can get away with the combination socket and switch with the “vertical” mounting points.