[Admin]

There is one easy way I can think of right now.

In functions.php, change this:

    $iforums=$DB_site->query('SELECT forumid,parentid,displayorder,title FROM forum WHERE displayorder<>0 AND active=1 ORDER BY parentid,displayorder,forumid');

into this:

    $iforums=$DB_site->query('SELECT forumid,parentid,displayorder,title FROM forum WHERE active=1 ORDER BY parentid,displayorder,forumid');

Now change every forum's display order to 0, and it will not show up on the main index, but it will be in the forum jump.

I guess you can add another 'special option' for the display order, let's say -1, but that would take more hacking.