Once you reach the lift don't pull the lever, instead jump on top of the fence (get on the fence by jumping on the giant air conditioner next to the box with the gas cans on the top of it).

Next jump on the other fence and walk a couple feet from the edge, get a running start and jump on the power box on the other building (be careful not to fall off!).

This only works over Xbox Live so only try it by yourself for practice because the AI (computer controlled characters) will just stay in place if you fall off.