Typically, when confronted with a size issue, I've taken Apoxie Sculpt and used it to fortify my armature. Then take the piece and literally bolt it to a piece of wood, so that the piece in question could be baked horizontally in an oven. I've got a pretty decent sized oven.
What you do is take two pieces of wood, screw them together at a 90 degree angle, creating an L. Then you take a third piece of wood, that's cut into a right triangle, and then screw that to both pieces fortifying the join. The long side down, you would bolt your sculpture to the short side which is pointing up and down.
Lay the piece in the oven, and bake slowly.
You shouldn't have any problems.
God so loved the fat people of the world, he gave them his only begotten donut.