That's a good question.
But read again my post. I said that it could be simple by simply having control of the aircraft while you are on the back seat. I don't see any reason why shouldn't I have control of the aircraft with my HOTAS if I seat on the back.
Is it unrealistic? Yes. It is a good solution though. Be able to fly (and fight) the aircraft regardless of which seat you are. Sure, some systems like MFDs, CDUs that really needs a mouse to operate faster and more efficient should be excluded but simpler tasks like controlling the A/C, controlling the autopilot, flaps, gear, lights, radio etc etc etc I think the most logical thing to do is to make them usable using HOTAS or keyboard commands regardless if you are front or back.