I've uploaded the Arduino code for the Wemos D1 Mini. Seems to work well enough for me, but no promises it won't burn your house down. I should also mention that the state-of-the-art seems to have moved from emulating Wemo Smart Plugs to emulating Hue lights, so you may need an older (read, outdated) version of the library.

STL files for the case are also available now. I've generated STLs for the lid both with and without the Jolly Wrencher, for anyone who might want to put their own art up there. If anyone is interested, I can put the OpenSCAD source for the case up as well.

I'll be adding build details and images soon, as there's some modification required to the relay shield.