I'm inclined to think that it's not based off of any actor in particular, but rather that the filmmakers just put in a sort of general version of Norman Osborn to serve as a placeholder until it's time to introduce his character. Also, by not showing many details about his appearance, it keeps with the character's current mystery factor. The silhouette wasn't very specific, so that they can reasonably cast any actor for the role when the time comes. I think the Norman Osborn character, or rather his off-screen presence, was handled very well in this film.