This was an attempt at making a belly which moved. The idea was that it would wrap around the back like a kind of belt which would then move up and down giving the character a greater feeling of weight. It didn't go ahead though as a single wire through the center would suffice.
This method uses a similar concept, a large piece of solid foam, encased in soft foam but with a single piece of shrink wrapped twisted aluminium wire attached into the core and armature with K&S. This allows for movement in the belly with a simplistic design, AND its detachable.
The rest was just simple padding out of the pelvis block, allowing for a rigging point into the back and a point in the front to allow the belly piece to be inserted. It's definitely worth glueing pieces of hard foam like this together before you sculpt the shape you want. As you could spend a fair amount of time sculpting the perfect piece for your pelvis/chest block just to find out it doesn't fit onto the armature.
The chest piece was done in a similar way, glued with a hot glue gun and left to dry in a vice. The shoulders were left free in order for the arms to remain detachable. This method, once perfected, will then need to be replicated on the ball and socket armature.