[galaxy-dev] External Pipeline Cleanup

Hi all - For various reasons, we've had to implement our pipelines external to Galaxy, but still give Galaxy the ability to run them. I've accomplished this by having the Galaxy tool wrapper call the external app to launch the pipelines. My problem is that when a user aborts the tool, the tool needs to be able to communicate to the pipeline that its need aborted. How can I do this? Is there some way to get a notification that the job has been cancelled before its actually cancelled to perform clean up?