I thought trinidad already had a usecase for this. In either case, yes, a configurator would be the right way to handle this although, in a portlet environment, session timeouts are largely irrelevant. The portlet handles the request and if the portlet's session has timed out, our portlet may not even get the request. For the full page case, this would be fine. For the PPR case, it may hose us.
In any case, what I would do in the portal case is, if we do get the request, I would either treat it like we have not timeout_url OR I would simply write out the redirect url to be the current action url. This will "try" to post an action request to the portlet, but then the portal will take over and prompt the user for sign in.
I have some code for a configuator which does something similar that I can forward you.