Yeah this is the kind of thing you want to fix before importing to Poser.  I don't know Sculptris but the thing you want to do is get the normals (the "outside-ness" of a polygon) facing the way you want, rather than using something like that twofaces utility (which as you've discovered, really only doubles the polygon count).  Then import that.  It's a real pain to try to fix this kind of thing strictly in Poser, much easier to just not import it in the first place.

I get the idea you're trying to do something like this?
http://sites.google.com/site/fleshforge2/Home/free-stuff/renderroom-prop

If so, you probably want to set the object display style for the sphere to "Outline" once you have the sphere placed, so you don't have trouble seeing what's going on while setting the scene up.

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