Hi Hannes,
You can imagine planar mapping and also the default UV layout as preset states of the flattened UV mesh.
But this secondary representation of your render-mesh can actually take any form you wish.
Inside the UV-Editor you can use any of Rhinos tool to deform the Vertex-Layout of the flattened UV mesh – this will consequently drive the texture appearance on your Nurbs model. I used Maelström on the UV-mesh to illustrate the case – using similar principles you should be able to massage the mesh vertices to the locations you need for your model.
In case your model is a polysurface you could create a somewhat simplified single-surface-version of your model or create a mesh representation of the model inside any mesh modeller and use this geometry to drive the texture projection via the Custom Object option – it’s essentially a texture baking operation between objects with deviating (render) mesh vertex count. Hope this helps a bit.
Grüße aus Kreuzberg, Holger