Spring WebFlow: Cleanup on HttpSession invalidation

If I need to perform some resource cleanup (deleting temporary files) upon Flow completion, including when the HttpSession times out, what's the best way to do this?

FlowExecutionListener.sessionEnding() is called when an end-state is visited开发者_StackOverflow中文版, but not when the HttpSession times out.

Is there a safe way for an HttpSessionListener to access to SWF scopes?

(Spring 3.0, WebFlow 2.3)