i don't know for sure, but can you step down your input voltage to a value say 9-27 V DC and then use the voltage regulator and then step up to your desired value?
Just remember two things, when driving a motor the input power is V_in*I and output power is V_backemf*I=Tw(w is the velocity and T torque), in any system you can not generate output power greater than the input power,so whenever the C-EMF is greater than V_in, its the mechanical load that is...