Some people (myself, in a former life admittedly) choose an overpowered car (read: Vettal), then get so far ahead that you can pull over for a bit, take a a nap, etc., while the race goes on. You can probably cut out 4 or so hours.
Speaking from experience, though, it's not worth spending that much time on something if you're gonna "cheat." Do a half hour every few days and by end of summer you will have finished, as well as mastered that particular track, and feel good about it.
Good luck!
Or get a few friends together and pull an all nighter!