This is a really cheap and dirty hack, but it works.

If you go to http://www.girlguidingbeaconsfield.org.uk/?p=25 and click ‘Read more at Bucks Free Press’, you can see it in action.

Download the plugin ‘wp-noexternallinks’ and edit’ wp-noexternallinks/wp-noexternallinks-parser.php’.
Replace line 9 with:

$sep=”.$wp_noexternallinks_parser->LINK_SEP.’=';

and line 72 with:

$this->LINK_SEP=’/external_link.php?go2′;

Then create a file called ‘external_link.php’ at your wordpress root. Add the HTML to the file, warning users that they are leaving your site, and then add a link as follows:

<a href="”>Take me to the page.

If this fails, let me know.

Also let me know if you find/think of a cleaner way to do this. It is amongst the most shameful hacks I have ever attempted.