for stacking dummy cakes of styrofoam you don't need any dowels, they are really light of weight. You can just decorate each of them (with fondant or RI) and at the end stack them and add the decoration. If you want them to stick well together just put a dab of RI between them.
Good luck with it!!
Lara
I've even hot glued them together - if I was icing them in buttercream.
After attaching them, ice and decorate away!!
Lately, I've been using royal icing to decorate the ones for display, as it holds up better. However you do need to work quickly to get them iced.
Good luck!!
Amy 
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