Could you use the ePoly script function which gets geometry verts based on a uv vert ID? That way you can just go through the entire set of UVW verts, get the related geometric vert for each one, and discard it if it already exists. Can't remember the exact command, I think it's in polyOp, or might even be an unwrapUVW…
I looked for it in polyOp but didn't find anything like that, so I went on to the unwrapUWV functions. one of the new functions in max2008 seems it could work. it's called "getVertexGeomIndexFromFace" but it says it's exposed via unwrap6 interface which I have no idea (and can't find) how to use same thing could go if I…