Went to a footie match on the last Saturday of the season.
Bit of a corporate affair, but we all drew numbers and stuck a fiver each in to a pot. Each time there was a corner the 10 of us shouted "corner!", much to the amusement of the adjacent boxes, and then the pot was passed to the next number holder. And so it went on for the 90 minutes and at the final whistle the person left holding the pot won the contents.
So for Le Mans you could use something similar for each retirement, be it mechanical or a crash? That theory will require at least one person staying awake, perhaps whoever holds the next number has to stay awake to get his/her hands on the pot and then wake up the next?
Just an idea...