I think Wilton has a castle kit similar to this, maybe there is a Frozen castle kit too.
AYup wilton had a castle kit, you can customize it by covering the towers with blue fondant and adding petal or disco dust to add shine/sparkle :) you can reuse it :)
I am part way through a Frozen cake myself and made my castle out of modelling chocolate over a polystyrene construction of a small dummy tier and cone. The whole thing is about 20cm tall...
You can see a picture here: http://cakecentral.com/g/i/3242269/work-in-progress-frozen-ice-castle-for-large-mountain-cake/sort/display_order/
What about Broken glass candy you can make?....something along these lines...you can create it anyway you need too ...and place it right. just type in broken frozen glass cakes to find cakes....I bought candy rocks for my cake I was going to insert it into the cake at angles...and instead put them on each side of the cake in cups....to show the theme....
http://media-cache-ec0.pinimg.com/236x/ce/90/8d/ce908d38ba7fdfc7c718dd43f835cce3.jpg
http://media-cache-ec0.pinimg.com/236x/87/b7/23/87b723d2986b39120fef660714f658a2.jpg
broken glass used in this home cake....
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