I'm not sure this would work, but you can give it a try. I would try making the bottom half of Hoot with rice cereal. I would use a little less marshmallow than the recipe calls for, this will give you a firmer cereal. Once it's cool enough to the touch, try and pack it down as tight as you can while shaping it into a semi-circle. The top part is cake baked into a large oven proof bowl. Make extra circular cakes to get the height you need. Make sure to use lots of dowels. I made a cake that needed similar construction, but the cereal was the top layer. I posted the picture if you want to take a look.