From an engineering viewpoint there's nothing simpler. Fit a bulkhead between ribs, made from a lightweight ballistic composite such as Kevlar, and a simple intercom / CCTV system so that the Captain knows what's going on up the back.
There's no need to block any emergency exits, since aircrew always have a route out the cabin window. The door in said bulkhead could be locked via a weight-on-wheels switch (that'll exist already for things like lift dump and thrust reversers), with some form of emergency override (a) on the cockpit side, and (b) outside the aircraft for crash crews.
There's likely to be some loss of revenue earning cabin, this largely depends upon where the furthest forward toilet is. A microwave and heatable meals are no problem.
So far as UAV technology is concerned by the way, I think most discussion had centred upon autopilot and autoland, so the risk of terrorists taking over some control room somewhere wouldn't be an issue.
G