When we held 2 hour QRA from home, for a normal hours scramble, it was not unknown for the odd stray to be roped in to shorten the scramble time.
I once intercepted a late arrival in the car park and pushed him straight onto the aircraft, goonsuit and head set following
Back on SAROPS, the SOP was for additional crew members to fly, for instance a pilot and a couple of extra AEOp, as extra eyes on the flight deck and in the beams as visual lookouts were supposed to be changed after 30 min (?). Notwithstanding planned launches, 24 crews etc, I was unaware of that ever happening.