Thankfully I have a picture to illustrate my thoughts. The grand staircase in it's current configuration has two parts. The main stairs leading up to a half level, then side stairs leading up to the actual station level. If you look you will notice that the platform actually has a great deal more room then the stairs utilize. It would take minimal effor to reduce the planter length, and incorporate an elevator INTO the platform. This would minimize the "stick out" effect, and utilizing the two door elevator currently in use in the parking structure the only visible element on the bottom portion would be the actual doors. This would also alleviate some of the congestion concerns voiced earlier. Obviously during parades the elevator would be closed with proper sinage posted on both levels.
Theming around the elevator would also be fairly simple as it could be themed to a ticket booth or luggage storage booth on the main platform with the door facing the station it would not even be seen from the outside. The only doors you would see from the bottom of the staircase would be the outside facing lower doors which could be painted in any of a variety of Victorian decor complete with stone work trimming the door itself.
Cost would be the main factor... but aside from that it can be done with minimal impact.