Hi,
This topic is raised in this forum time to time. A small tutorial explaining, how to use an external audio editor,(for destructive editing),under ardour environment, can be found here.
http://www.keepandshare.com/doc/2193359/ardour-external-editor-pdf-august-29-2010-4-36-am-1-3-meg?da=y
It is for linux+ardour. New users may find it useful for them.
Cheers.