jakejohnsonusaGTA

Open the main.scm with a program. (Sabby Builder or Mission Builder work) then locate the parked car locations. I don't know the exact one(s)... you'd have to figure that out. It will look somthing like:
014B: $2335 = init_parked_car_generator 417 -1 -1 1 alarm 0 door_lock 0 0 10000 at 383.178 2538.891 16.53 angle 180.0
014C: set_parked_car_generator $2335 cars_to_generate_to 0
Delete both lines of the parked car. NOTE: the "at ... angel..." will tell you the exact cars location to help you find the right car park files.
Use: http://www.gtaforums.com/index.php?showtopic=195055 for help. Just do the opposite.