- He asks for Molly's help
Sherlock comes to Molly saying he needs her help because he thinks he is going to die. It helps fake our own death outside of a hospital whose coroner is in love with you. - Rubber ball to stop a pulse
As Sherlock waits for John inside of hospital, he bounces a rubber ball against the cabinet. If you place a ball in the armpit, it can stop blood flow to the arm and no pulse can be felt at the wrist. As John approaches Sherlock's seeming dead body and reaches for the out stretched arm to feel a pulse. When John feels no pulse he is convinced that Sherlock is dead. - A well choreographed fall
As Sherlock talks to John from the rooftop, he makes sure John is standing behind a building so he cannot see the road. John sees Sherlock jump from the building but does not see him land.
When you see Sherlock on the ground, a truck full of bags can be see parked right beside the body. The fall from the truck bed to the ground is at most 3 feet. He landed on the bed of the truck and then rolled on the the ground.
As John runs towards the hospital, a biker runs into him and knocks him to the ground. John does not see the truck pulling away. Sherlock has a network of homeless people and could easily have paid someone to knock John over.
By the time that John gets to Sherlock, the truck is gone
Easy peasy.