No offence, but in no way is that a solution because you have only limited control of getting in that situation. A real solution would be be a real reverse switch. E.g. put it in reverse, use the throttle to move the car, put it back in 1 and go. Just like a real car.
But you're absolutely right that the extra effort it takes is negligable if you are forced to reverse, your lap/race is screwed at that point anyway.

Besides, all you have to do is press a different button, it's weird and not like it's done in a real car, but I doubt it will make a significant (if any) difference at all where laptime is concerned. Actually, now that I think of it, this single-button solution may be faster, since it requires only one button press.