What ever you dont charge by tacho time, charge take off to landing. The problem with charging tacho on a turbo is people rush the warm up and cool down to save money and thats when the damage happens.
We had problems on the twin with the same thing, switched to take-off to landing and the problems virtually vanished. You will find that as people or paying airborne time they are actually very honest and in a small group it is easy to put checks in place to ensure that no one is being dishonest.