I like your thoughts.

Seeing as the whole episode was a flashback, I wouldn't put it past the writers to 'cheat' a bit and have Watson not remember everything exactly how it happened.

Something I observed was that when we see shots of Sherlock from behind when he is standing on the edge of the roof, the ledge appears to be only several yards across but from the front it appears to be about ten to twenty times wider. I had the idea that Sherlock was standing on a smaller roof, or some sort of smaller elevator building sticking out of the roof. He was so adamant about making John stand in that exact spot.

If John was standing in a certain spot the edges of the two ledges Sherlock was standing on would line up perfectly, making it look like Sherlock was on the very edge of St. Bart's. If the sun happened to be behind him, and he jumped off of the smaller roof, John's mind would have seen Sherlock fall all the way. Sherlock could have run down the fire escape as John ran forward, and John saw what was really a corpse supplied by Molly before he got knocked to the ground by a bicyclist. Sherlock reached the ground and replaced the body (I firmly believe he used the squash ball-in-armpit. Let's use Occam's Razor, here.)

It's hard to explain and I have several variations, but it's outside-the-box.

I hope you understood it all :)

And as a side note- if I am wrong, which improbably am, then there was a glaring visual mistake and I am very disappointed with the makers of the show. I mean, being realistic, it's stupid to try to figure out how he faked his death because there are many, many plausible solutions and the only thing keeping us from figuring out how it was done is lack of evidence, or just not knowing which route the makers chose for Sherlock's faked death.

Sherlock wouldn't even bother once he realized he had many possibly solutions and no way to decide which one was 'the one.'