Creating level set from "hollow" mesh?

[Tom Hudson]

Is there an existing mechanism to convert a "hollow" mesh to a level set which includes the interior hollow region? For example, say I have a mesh that consists of a large sphere with outward-pointing normals and a second, smaller sphere with inward-pointing normals sitting entirely inside the first. If I convert this to a level set using meshToLevelSet, I get a level set that consists of just the outer sphere -- not the hollow interior region.

Just wondering if this has been handled somewhere. Thanks!