A good start would be getting paid for the time preflighting the aircraft.

Why not block + 30 minutes of pay for each leg or something like that? Its a start and more accurately recognizes the work you have to do. Two 4 hour legs and Four 2 hour legs pay the same, but are drastically different amounts of work.

I consider preflight prep to be one of the most important and critical phases of the flight, and you're not paid a dime for doing it.