Sharon - from Kansas City, MO
One or more of the layers can be "dummies"; bakeries often do this! Most dummies are made from Styrofoam cut to the size the actual cake tier would be. You would prepare the Styrofoam for stacking just as you do a real cake (i.e. - add dowel rods which separator plates will snap into), then you ice and decorate the dummy with the same icing you use on the cake. If the tiers will not be separated by pillars (that is, one tier sits on the tier below it) have the real cake on a cake circle or board.