You could bake it in a mixing bowl. I've done that before, the 2 quart pyrex bowl works well but the bigger one it's a little iffy getting the center done.
I think from the description in the blog that she lined a bowl with buttercream, put the baked cake layers in with more buttercream, and then put the whole thing in the fridge to firm up. Once it was hard, then she could set a cake board on top, flip it over, unmold it and then peel off the plastic wrap, then cover the cake in fondant. I think you would end up with a lot of buttercream on the cake that way.
I wanted to try making that cake for my daughter's birthday because she wanted a turtle cake, but what she really wanted was little fondant turtles on top of a cake, so I didn't get to try it.