Could a quadrotor use a main gas powered rotor with small electric rotors for attitude control?
Early versions of Sikorsky's VS-300 helicopter prototype used something similar to what you're describing, as his first attempts had three rotors on the tail boom, one vertical rotor for anti-torque and yaw, and two horizontal rotors for pitch and roll. 



Of course, if you're already using large main rotors, you might find, as Sikorsky found, that cyclic pitch control works even better and eliminates the need for the two horizontal rotors.