I was going to suggest something similar to Bill: Put a circle of parchment paper between the cake and whatever you sit it on to decorate. Then refrigerate the cake until it’s rather hard. Then move it to a flat surface that will fit in your freezer (I sometimes use a couple layers of frozen pizza cardboards). Freze the cake, wrap it well, and KEEP IT ON THE CARDBOARDS so it doesn’t “settle” and lose its flat surface. Then, when you’re ready to thaw, unwrap, remove the parchment and put on your carrier/server. Rewrap and put it in the fridge to thaw. Unwrap and bring to room temp.