actually, jumping off the train tracks is the way to do it...at least that's the trick i used. they key is jumping from the right spot so that you can actually make the distance easily. if you walk down the tracks until you're right above the taxi building, you'll see one of the support beams from the tracks that sticks out the side. jump from that beam (with a running start) instead of the track itself, and it gets you that little bit closer that you need in order to land on the roof of the pharmaceutical building.
give it a shot...i'll bet you can make it from there