i'd tried to find a way up there a year ago open PS2. everytime i drove by i felt like my dog had just been shot, because i knew i could never get up there, for 2 reasons:
1. there's nothing in the area that you can get a high bump off of
2. regardless, they're too high. you'd need about 120ft of height to land up there.
EDIT: i don't think you'd be able to get up there from the roof either, even with a PSB or BBM. besides needing about 70ft of height you'd be hard pressed to get enough speed on a short run-up.