Don't you wish you could do this stuff out on the open road with your own vehicle? Alas, it will remain in Gran Turismo 5 on the PlayStation 3, where slipstreaming and drafting is totally possible (and legal). See how to earn the gold trophy on the ninth test (B-9) of the National B License Tests. To unlock these tests, simply buy your first car.
B-9: Overtaking Using Slipstreams
Slipstreaming / drafting in these types of tests is CRUCIAL. You must follow directly behind the car in front of you until the last possible second and then slingshot around them. Try to stay as close to the side of the car as possible in order to get into the slipstream of the next car in front of you.
Move the car you're passing out of the way by crowding them if needed as they will usually move over and allow you better access to the next slipstream.
Note * Played with a regular six-axis PS3 controller.