A GPS has to be a better way. If a rider is going to fake it then they pretty much have to do it for 365 days on the trot. On my Garmin(s) I'm sure the thing auto sets wheel diameter from the GPS data, and not having the sensor attached doesn't affect the distance travelled, just the maximum speed.
Despite that, I don't like reading about Kurt having problems. It's not how this should pan out, which, ideally, will be based on the athletic ability to ride hundreds of miles every day.