Never heard the one about the wax. Maybe that would work.
I had thought about drilling into the nut and then using progressively bigger drills until I can split open the nut and get the bolt out that way. I am sure I can then find another square nut to replace it with.
Also, I thought I should try to get something down the right hand side of the nut - there is a lot more plastic on that side and maybe this would hold better. I will try that in the morning.