Artman21 has released an update (version 1.0.2) of the system preference pane, JeditAnywhere (http://www.artman21.com/en/jeditanywhere/), that lets you edit the selected text in mailers, word processors or other applications with the Jedit X text editor..
With JeditAnywhere, by tapping the option key twice, you can invoke Jedit X and edit the selection without the copy and paste operation. After you’ve finished editing, tap the option key twice again, and the results will be written back to the selected area of the target application.
JeditAnywhere requires Mac OS X 10.5 or later and Jedit X Rev.2.20 or higher. It costs US$12.