New URL in "Shipping method properties"

I don’t use any of the built in Shipping processors, but I would still like to store the tracking number in the correct field.



Then if someone clicks on the tracking number link on the order, it goes to a b[/b] URL specified in the “Shipping method properties” screen.



e.g.



http://www.royalmail.com/tracking/number/{TRACKNO}



Where {TRACKNO} is replaced by the tracking number.