Ganache by pouring before fondanting a cake
There is no reason pouring ganache wouldn't work for this. 50/50 cream to bittersweet chocolate will work just fine. Just move quickly while the ganache is warm - you shouldn't have any problem at all.

here's a picture of a cake iced by pouring 50/50 ganache:



50/50 poured ganache sets firm in the sense that it stays put once it has cooled. Considering the carving that your cake is going to require, and the fragility that I would expect in the cake, I'd definitely go with a liquid that is more pourable than the icing in your picture looks to be. 50/50 ganache slices just fine. Look at the cut out in my picture. The slice through the ganache will just as "clean" 48 hours later.