Not a cheat as such, but if you want to beat your fastest time trial lap without having to do a whole lap to get a "Flying lap" time, simply start the time trial and instead of starting as usual, reverse back around the last corner and go back to the second last corner, then start from there and you will have the same speed going over the "Start Clock" green line as you would have on a flying lap. You still need to do a flawless lap, but it saves having to do a whole lap just to get a flying lap time.