This is made much easier if you are able to play a private match with a couple of friends/boosting partners.
You can change the settings in a private match as host, by going to the cog icon on the map's image in the lobby, in there you can turn on the setting so that all vehicles are already repaired.
You don't need to find the keys for the car or anything, just jump in a vehicle and leave your friend behind.
I would suggest Crystal Lake Small or Higgins Haven Small for this