Really simple. Select Time Trial, any new track for you, any car.
Start your run and immediatelly brake and stop your car for 10-15 seconds. Gas on and finish one lap. Hit Menu and exit race.
You will now have a personal best time.
Then, Time Trial again. Same track, any car, but select to run against YOUR PERSONAL BEST time. Start your run and "park" your car inside your ghost for 5 or more seconds.