To slow down opponents in either standard, elimination, and duel races, push into the back side of them while next to them. If they begin to turn away from you, stop turning or you will start spinning. This trick works best by pushing into the bed of trucks on the off-road levels, and into the Taurus stock cars.
Enter GIMMEGIMME as a name in career mode.
Start a new career and enter MARK MARTIN as a name. Go to the first race in the KA series and do the qualifying and then the race. Your car will be invisible.