closed model and uv mapping

My problem is the following. For a closed model, some vertices own one uv while others own two uvs. it would be simple enough to duplicate a vertex, so that we keep both uvs, but we are essentially not a closed model anymore. This creates some special cases when we do things like sillouette finding and such (for toon rendering.. shadow volumes.. tons of techniques). I beleive Milkshape/3dMax duplicate vertices. Another way I was thinking was to draw an extremely small quad which will keep the model closed, yet allow vertices (duplicates) to have different uvs. The problem with this is the complexity on the model loading side. It is also possible to mark duplicate vertices, and keep my triangle information somewhere else. Thus when I traverse my triangles I am able to identify duplicates, quickly refer to them, and find the correct adjacent triangle edges. Does anyone have a "clean" solution for this, something simple and enough so that we don''t have special cases lying around?