I have the feeling I'd seen this video before: an attempt at the Sikorsky Prize with a giant super-lightweight bottom-rotor quadcopter - a sort of Ekranocopter, or Caspian Gym Monster.
Somewhat predictably, there's a great challenge in getting the rotors out of ground effect - hey, why do you think they're on the bottom?
Also, there seems to have been no consideration given to controlling the thing, so naturally it drifts off station rather quickly. (For some reason, the guy sitting in it is given the title "pilot" when in fact he's merely the engine.)
A stabilization system would add a few pounds (mainly in actuators and bearings) and a bit of drag on drive system (assuming it's supposed to be all human-powered). That, and making the span even biggerer to stretch that ground effect for all it's worth, and a big dose of performance-enhancing drugs for the engine... and perhaps filling the gym with a xenon-oxygen blend... and perhaps the grand stunt could be pulled off?
Oh, here we go: story. Apparently I hadn't seen that particular video before; it just looks awfully familiar.
And, yes, it is supposed to be human-powered, so getting the Librarian to pedal the thing would be out of bounds.
Afterthought: actually, a control system need not weigh that much. Quadrotors are normally controlled by differential throttling, so it's merely necessary to have some mechanism for adjusting the relative speeds of the rotors. So, some sort of four-way CVT, of rather limited capability, should do the trick.