Can you do like the cake-decorating people do........use round 'plates' supported by internal dowels to stack as high as you need???  Watch an episode of "Amazing Cakes" on cable/satelite.  The pros hold up multiple layers on the big impressive cakes with cake stands......dowels for legs and rounds cut out of plastic board to set the actual cake on.  I'd check with a local cake decorator to see how to make the icing as stiff as you need it.  Or Google "fondant" and see if that might fit your purposes.  It isn't the easiest to handle, but may be suitable for what you're trying to do.  Good Luck!!!!