I finally got round to scripting IE to use BBEdit as the 'source viewer'. I'm using a combination of a Studio Log: Script Snippet that takes the source of the front window in Internet Explorer and opens it in BBEdit and the latest version of DragThing to bind the AppleScript to a keystroke (F11). If I wasn't a registered user of DragThing I'd be tempted to use Key Xing to do much the same thing. Works like a charm.