I don't think they took bits from the internet & cobbled it together - I think they pretty much knew how he did it when they filmed it.
Why would Sherlock be bouncing a squash ball at all if it wasn't going to be key? And there's only one way it could be.
Also - Sherlock is not some mystical super hero. He's a human being. If you jump off a roof of that height and survive, there's actually only one explanation - your fall was broken by something soft. This must have been the explanation they had in mind when they filmed it.
The only bit that jars is Molly providing the body of the lookalike. This makes no sense to the narrative because it wasn't necessary. Sherlock could just have lay on the ground initially, with the Homeless Network covering him in blood when John was lying in the road.
I suspect this was to give Molly something visible to do, rather than just say that she faked records off screen, since she was supposed to be so important to the whole plan.
The bits they did cobble together afterwards were the two fake explanations, which they'd obviously based on fanfic stuff they'd read - and that was a nod to the fans & acknowledgement of all the interest.
But - I reckon there's still more to all this. It can't be a coincidence that the man trying to blow up Parliament was called Lord Moran. SM was a pretty important character in the books (the 2nd most evil man in London, after Moriarty) and it seems odd that his name was used here.
If SM was still active - then maybe Moriarty is too? Also, "Lazarus"?