Hrrmph.
So I made a deathbox, but it's not as automatic as I'd like. I'm quite proud of my power supply for what is essentially the perpetual waterfall device, except with magma.
Top layer: Control windmill
Second layer: Control gears & other power-supplying windmills
Third layer: Perpetual magmafall pump arrangement
Final layer: Customer Processing & control levers
So Disgruntled Customer is told to pull the bauxite lever in Customer Processing to have his issue addressed, at which point the door locks him in, keeping him on top of the lever.
Then is the annoying micro-management part as Urist McBureaucrat is told to pull the blue lever outside Customer Processing. This activates the inactive control gear on the second layer, connecting the power from the Control windmill on the top layer to the inactive screw pump on the third layer. Sounds complicated, but this hanging gear assembly arrangement allows the whole thing to be turned on and off at will without disassembling the control windmill.
After Disgruntled Customer's complaints have been heard for long enough ("Well, you see, Urist McPleb has a better dining room thaaaaAAAaaaAAAaargH IT BUUUURRRRRNS!!!!"), the blue lever is pulled again, stopping the magmafall safely, at which point the grey lever is pulled, opening the door and allowing for final processing of Disgruntled Customer (who should just be a neat pile of bones by now).
While I like my power switch that doesn't destroy my windmills, I think the operation is far too fiddly. Any suggestions for automation?