I've heard that some flight schools allow non-pilots to rent their aircraft, provided a "flight school approved" pilot is going to fly the plane. However, that pilot can in no way be employed by said flight school.
The flight school at that should produce a legal document that has been drawn up, outlining the aircraft renter's obligations and responsibilites, stating that the renter understands that the flight is being conducted under part 91, that the renter is responsible for the airworthiness of the craft, etc etc, and have the renter sign their name on the dotted line. It's legal according to several well-established charter pilots I've talked to. The crucial point in this scenario is that the pilot cannot in any way be employed by the company renting out the airplanes, and the paper trail of payment for rentail of the aircraft cannot go through the pilot. In other words, aircraft rental payment and pilot payment must be completely seperate.