Ha ha. I figured it out!
I simply need to cast mVehicle to a car, bike or truck where i call the factory.
Vehicle myVehicle = myVehicleFactory(String typeOfVehicle)
if my type is 'bike' then i do this:
Bike myBike = (Bike)myVehicleFactory("bike");
or if it is a truck
Truck myTruck = (Truck)myVehicleFactory("truck");
and this now NOT completely polomorphic but you can kinda use other techniques to determine the concrete type you want to build.