The picture helps, thanks. This can be approached analogous to the thread remove holes.
Note that if you intend to draw just polygon shapes rather than circuit elements, it is better to use nd.Polygon() objects in Nazca and the nd.geometries module for geometry helper functions, instead of nd.strt() and nd.bend() structures. In the former case, one can manipulate polygons directly with the nd.pyclipper module. Also check out the merge_polygons function in the inverted MMI tutorial.
In the “bend and strt” case you first have to pry the polygons out of the bend or strt cells. Note also that bends and strt are circuit elements, which have a much larger overhead associated with them. This becomes more noticeable when you use (very) large numbers of them.