"If the building is made with a lot of metal, you may be effectively completely blocked. Any chance of mounting both antennas high enough so you do have line of sight ?"
Looks like it might be metal - here is the building in question.
I have been using elevation maps to calculate how high the antenna must go to clear it. Quick calculations show an antenna 25ft from the ground (easily done with a chimney mount) will clear it. My next step is to borrow an accurate GPS unit to get super accurate elevations. I tried today with my iPhone's built in GPS but it's just not all that accurate for getting elevations.