Coudl yo not create a /prosthetic' piece to fit over the holes? select the polys around the hole in Poser, spawn them as a prop and export it into your modeler of choice. Close up the holes, import it back into Poser and use the dragoceros rig as it's joint setup, then add it as a character. Now you should be able to conform the prosthetic to the original figure.

I'm not sure creating a morph where you actually delete and add polygons is possible - or am I completely wrong?

JonTheCelt