Just what kind of company is this? Have you tried individually telling peole not to do this and if they do they are stupid? I'm thinking the insult route might help.
Even if you were to adjust the box so you put the power switch on the inside, you have already found out that they will simply unplug the boxes.
Crazy glue the switches in the on position and the plugs to the wall?
Start by covering your own arse and sent memos the other way, up to managment. Explain that users are not following procedure and are risking the network. Anytime you tell execs that their network might break, they worry.... Put tape and notes all over the boxes, power switches and wall plugs saying "Do Not Remove/Power Down Systems! Call so-n-so for assistance."