It is possible to access a portlet session from a servlet in the same webapp. You need to pass the portlet namespace in the request to the servlet, and use that namespace to find the portlet session in the "global" session, which is nothing more then the normal http session. The JSR 168 spec defines the pattern to "hide" portlet sessions, I don't have the exact format at hand, but its not difficult to figure that out.
There is still another, bigger step involved to restore the faces context with that information, but at least its possible to access your managed beans with session scope, which may solve your problem.
