I figured out that you can use the lap timer; if you stop right at the line, then hold the car, floor it, and release the brakes, you can launch it and the timer will start just as your car passes the start line (hopefully the moment it starts moving), Then you pause the game the moment the car hits 60, and estimate away.
I have a reviews thread on which I am going to review the GSX/4 (Car Reviews by beeblebrox237), then I am going to modify mine. It could really use the wing from GT Auto, as the rear end is a bit loose at high speed.