tilt switch to activate power socket
The ultrasound idea from @Robert Fay is a great idea!

Assuming that you are not looking to design a PCB for producing 85 units, this is something that you could build using an Arduino or similar. It might be a bit tedious to build 85 times though.....

You could use components such as: 


https://www.adafruit.com/product/4007 (Ultrasound distance sensor)
https://www.adafruit.com/product/3191 (Relay capable of switching mains power)
https://www.adafruit.com/product/2771 (Adafruit's Arduino compatible board that will stack neatly with the relay)


Put it all in an enclosure with some holes in the right places and there you go!

You will have to write some code but there are plenty of tutorials online that you can use.