Help with Wedding Cake

I am making this cake for a wedding reception on Thursday afternoon but with only three tiers.  The bride has now decided that she wants the tiers to be "floating" as in the picture instead of stacked tier on tier but she doesn't want columns.  Could I use 1" foam core, cut an inch smaller than my cake and glued to the bottom of cake board or would it be better to use hidden pillars.  I would like to put a dowel through all three tiers for stability for transporting (may not matter since it's going to be 100+ degrees on Thursday). The tiers are 12, 9 and 6.  Is there a better way?  Help!