The CAD template from the relay box was reused here. This time it didn't take an hour to design and fabricate a one-off part.

Test milling on the blue foam. This stuff is so awesome for prototyping that I have a pile of rough-cut slabs on my stock shelf.

Milling for real. The pen outlines were just for rough reference.

Assembly.

All done.

Of course, I could have just bought one at Enco, but this was more fun. And the specs on mine are actually better.