Since the type of united edges you want is not implemented, there is nothing in the documentation. The standard trick is to replace the original edges with dummy point nodes and various axis-aligned line segments. If your input graph satisfies some simple constraints, this process can be automated. As an example, one can use the following pipeline, which uses dot to position the nodes, gvpr to create the auxiliary graph, and neato to add the edges and create the output:
 
  dot orgChart.gv | gvpr -c -forg.g | neato -Tpdf -n > orgChart.pdf
 
Here are org.g and orgChart.pdf.