I’m going to risk saying after watching over in slo mo: this appears to be not fake as the MSM are apparently saying, but a deliberate jump, not a fall, if you watch closely, he appears to touch the window gently with his left foot, as if to gain a little momentum, then he swings his right leg out to make the swing increase; at the same time he lets go with both hands.
One sock on and a rope maybe a little Entered Apprentice play? after he falls he is reborn; dunno, he may see a softer landing below him than we know of and swings out to clear the other stonework, though I can’t see it being fake.
Either way you Look, nothing should surprise.
Update 5ht March 2015: Yep,told ya; http://www.out.com/popnography/2015/3/03/naked-man-seen-climbing-out-buckingham-palace