Apparently there is a garbage truck that's parked there and immediately drives away. You can see a glimpse of it if you pause. So the theory is that he did jump himself, but landed on a pile of soft garbage bags inside the truck, then got out and placed himself on the sidewalk, in the short time that Watson was delayed by the bike accident (staged, of course). He would then pretend to be dead (as did Adler in an earlier episode) and Molly would help him get out of the morgue.