In the earlier 22s you could pull the instruments circuit breaker and that would stop the clock. I think from memory you would lose oil pressure guage and a few others, maybe cht, but the oil pressure light would still work if oil pressure was low.
As stated before information on the operation of this r22 feature came out of the "mustering" section of the flight manual.
Of course there is a downside to using this handy feature and that is that the blades depart the aircraft in flight.