I'd make the smaller cakes dummy's out of styrofoam and treat them as if they were pillars between my tiers. Put my larger cakes on square card boards on top of square cake plates as you'd do any cake stacked with pillars. I'd run a dowel up the center to help anchor the styro layers, place dowels in my real cake layers under the styro as usual as supports. Replace the lost servings where the styro tiers are with cakes in the kitchen.
As others said, I wouldn't do this out of butter cream (that would greatly change the over all look/intent of the design, plus it will kick up your level of difficulty greatly).................if I HAD to, I'd frost the cakes in butter cream but then do all my decorations out of fondant. The decor is so much easier out of fondant (you'd save sooo much time) that I wouldn't compromise on that issue with the bride at all.
Edited by Stitches - 1/13/13 at 8:13pm