MazKid mentioned this in a thread many months ago. However, as he stated, in only works well in the lower-powered cars-- In those instances, tapping reverse will sort of send the transmission into neutral, then give it a kick into the next gear. With higher-powered/thin powerband cars though, it's definitely not something that you want to do in a race.
you probably could do that if u have a GT force or driving force (i think that they are the same thing) when u are drifting because it won't shift when u have the wheel turned so far.