So I've been very suspicious of the crowd of people, John's fellow witnesses to Sherlock's fall (aside from the biker and the truck driver, I mean, we must be pretty sure he paid them, right?)... I mean, even Moriarty commented on them, and they're very insistent about keeping John away from Sherlock, aren't they?
This clinches it, though: there's a young doctor taking Sherlock's pulse at his neck. Going off of the assumption that he used the rubber ball trick, the pulse in his neck would be active. (You'd need someone taking the pulse there, that's the best place to check, and if someone's hand is already there, John has to go for the wrist.) ...THAT GUY'S SO IN ON IT. And maybe some of the others, and those paramedics must have been in on it too. ...You'd need a doctor anyway, to declare him dead, so I suppose one doctor should've been a given from the get-go.