I love that cake!
I did something similar on a display cake. I took masonite boards and used small round plastic pieces glued to the center to make the space in between.
I really like that cake. I can't wait to see your pictures when you get this done.
I'm sorry I don't have any advise on how to do this, what Lenette said sounds perfect to me. I just wanted to comment on how beautiful that cake is. It's GORgeous Props to the decorator!