It's impossible to get a shot of this without people on it. I think you would have to be the first through the door in the morning and rush around to the exit, just to get a shot with an empty staircase on it.
Personally, I cheated and used a gorillapod and a neutral density filter at f/22 and ISO 50 to get a 20 second exposure. Along with a very small amount of 30% flow cloning in photoshop to get rid of the residual 'people trails'. Highest rating 92.1