I have not figured out how to do it, but if I were set on doing it, the easy hack would be to fool the system by setting the wheel size smaller. Of course, everything your console tells would be off by as much, rendering it useless. Meanwhile the wind blows through your long golden locks as you frolic along enjoying speeds only your beer swilling friends can tell you from a speedometer of a '67 Mercury trailing alongside on a country road, full of potholes and vertical grates.