Metaballs/Connect centerpoints, if they do not intersect with borders

Hi everybody!

I want to connect the centerpoints of several metaballs if those balls are smoothed together, which means these new lines do not intersect with the borders of the metaball. I already tried to deal with the containment component, karamba´s nearestneighbors and tried to cull lines which intersect with the metaball borders but i had several problems with the data structure as every point is contained by a certain curve and i tried to do this in a more complex 3d-metaball structure with several different centerpoints. As i show in the attached image, the three points at the bottom should be connected by two lines...the others not because these new lines would have crossed the borders of the metaball. Any ideas for solving this problem. Thanks in advance!

David