I have seen several cakes on her made from a dummy cake. I know that they are made from styrofoam and fondant but what do you use to stick the fondant on? Is it actually icing? If so how long will the dummy cake last?
A light mist of water will do the trick fine, especially if you want to pull it off and re-use the dummy. Others use piping gel, icing, crisco...but water is free!
Dummies last a long time, the only thing you need to worry about is color fading (from light) if you want to keep it.
do not use water!!!! if you intend on jeeping them for periods of time the bacteria between the layers witll eventually grow mould and discolour the fondant, vodka is the best thing to stick fondant to dummies, it dienfects, evaporates, fondant does not absorb it like it will water which will make you fondant start to break down, and you wont get any scary bacteria growning between the layers!!!!
I only make dummy cakes and use a light misting of water to stick the fondant to the styrofoam. I have never had a problem with mould. The key is using just a bit of water. Some of my cakes have been sitting for 2 years with just a plastic bag covering it to keep the dist off and there has been no discolouration.
A light coating of clear piping gel works very nice as well.
They keep for a VERY long time. Keep in the dark and out of humidity. You will have to dust them every so often, too. The light will fade them in time....