My wife is a retail Mang. Try to find "Glue Dots" like hot glue but you can just peal and stick!!! Be careful of suerglue because of the "hase" .
I would not glue the car to the mirror. Try putting the car on a raised clear surface, and maybe slanting the mirror just a little. You can see much more, and with less hassle on the judges part.
Or, put the car on dice, bolts, crome lug nuts???
Just a couple of thoughts to think about.
Jimmy.