[Boost-users] [BGL] adding an edge without modifying a graph?!

Hi, The subject sounds crazy, I know. But I need to add reverse edges so I can run a max-flow algorithm on my graph, and I would not like to modify the input graph. I can make a copy of the graph, modify it all right, run a max-flow algorithm, and discard the modified graph, but that would be inefficient. So I wonder whether someone could share some trick on how to do that, if this is possible. I was hoping to use boost::subgraph: create a root graph, create its subgraph, and then add reverse edges only to the root graph. Unfortunately, these edges also popped up in the subgraph. Thanks & best, Irek