How can I deal with insurance requirements for flight hours and training in order to carry passengers?
The flight school might issue a waiver of that policy but it’s going to be based on a number of factors, including instructor opinion of your pilot proficiency on rotorcraft, time in the particular type you want to rent, and whether the insurance company can do this for you.  I’ve had to do that during my flight training when renting high performance and complex airplanes which had certain minimums set for their solo operation under the terms of the school’s insurance policy.  Ask to speak with the chief flight instructor for the school and see if they are flexible with a similar arrangement.  If they feel comfortable with your skill and proficiency in operating the R22 and R22 and you have at least a few hours in each type, they might just approve this.  Again, this is largely their insurance company’s call and not the flight school’s.  I’d guess the school gets discounted rates for insuring their rental aircraft by requiring pilots to undergo factory authorized training programs.