How can you add 20,000 miles to a digital odometer QUICKLY?

I'm installing a replacement instrument cluster(with electronic speedometer/odometer) from a parts car but it has more than 20,000 less miles on the odometer than my car. I've got it hooked up to a function generator at 1800 Hz which has the speedo at 160 MPH. At this rate, it will take over five days nonstop to add 20,000 miles! Is there a faster way? If I increase the frequency will I burn out the speedo motor? On the other hand, if I let it run nonstop for five days at 160 MPH won't that burn out the speedo motor? Should I maybe let it rest every 12 hours for an hour or so? I understand that new replacement odometers can be set to any mileage by pressing the trip odometer reset button in a certain sequence, but isn't that only a one time thing?