Sorry IOF for adding to the thread-wander ... But I agree with doing it simple - that's the way I roll. I there's an easy way to do something without torching my hard-earned goods, then I will find it. If it were me, I'd just grab a heavy-gauge extension cord (10awg or better), cut the plugs off it & wire it right into the box. I'd probably install jumper-cable clamps on one end for a quick and easy shower .....
....... like I did when I had a weeks worth of wet clothes and needed to get a pile of work finished. Might be scary, but if done properly, using a little common sense it gets the job done. My house is still standing: