The afterburner runner is easy, but what component is the starting block?
The starting block is the rear cone behind the turbine where the thrust 2419 lb is applied. Literally, it is the frame of the engine that is pushed. I don't understand why you say «apart from a divergent nozzle section». Isn't it good enough? To me, it's like saying: «In a car, apart from the wheels, what component transmits the force to the ground?» Nothing. There are only the wheels.What component (apart from a divergent nozzle section) transmits the afterburner's force to the airframe?
The turbine doesn't see additional back pressure. The beauty of the system is that the energy is instantaneously transformed into an increase in velocity instead of of an increase in pressure. It is the "kick" due to the acceleration that pushes the engine. The pressure wants to increase, but before it can happen, the gas particles are already gone, so it doesn't. But the force did exist, otherwise the acceleration wouldn't be there.The turbine can not see additional backpressure and the cone may be too far upstream.