False Capture,
Yep, that works - bit difficult negotiating controlled airspace though.
Many years ago, my club did use hobbs as the basis of charging of one of our aicraft. The master switch ploy was one reason for reverting to tacho, the other reason was that the more unscrupulous renters were simply flying the whole trip with the throttle against the firewall. Get there faster and, therefore, cheaper(!)
Not their problem if the engine wears out a bit quicker.....
WP42