If you don’t want to bother with registration, pm Elliot (slwrthnU)
I think he drove a car from FL on his mom’s car’s plates.
Oh and I should add, having done this a number of times myself.
The major illegality is no insurance, which is a “felony”, and insurance is rather easy to get, takes 15 minutes on the web.
Registration, if you’re caught without a proper one is simply a fine. Plus the cop will be very lenient towards your situation if caught and you show proof of insurance, which at least implies that you attempted to move towards legality.