After backing up your include/functions.php file you'd need to tweak both the draw_sites function which starts around line # 1175 and the draw_search_sites function, around line # 1347
Line 1234 for example
<a target=\"blank\" href=./out.php?ID=" . $sites_array[site_id] . ">";
<a target=\"blank\" href=\"'.$sites_array["site_url"]. "\">";
BUT,, and there is always a but, since outbound clicks would not be counted, the whats
popular page would be meaningless, so it would need to be removed from the navigation.
Despite what is commonly believed, the method of linking to a site via a file like out.php which does a 301 redirect is seen by Google as a back link from your site to the remote site.. but of course no one believes this.
Do a Google search for "link:http://www.freemusicvideosnow.com/" (that's my music video site btw) It is listed in the demo install here on Dew-Code and is indeed seen as a back link from here http://www.dew-code.com/demo/directory/3.html