Building nested FSM with BGL...

Has anyone already implemented a nested Finite State Machine with the Boost Graph Library? (Or a Petri net for that matter.) The thing that really puzzles me is how to implement the nesting, i.e., all nodes in a subset of the graph react to the same ``events'' from the ``outside world'', but I want to avoid making all the edges from the ``outside world'' nodes to the subset nodes... Herman