Well, OK....
You'd have to turn on debug mode to add the setting. Let's say you call it "yoursetting" and you put in a series of forumids, x,y,z. You now have an array which you will have to explode in a plugin to use:
PHP Code:
$yourarray=$vbulletin->options[yoursetting];
$yourforums = explode(",", $yourarray);
Then you can use it in a conditional in your templates:
HTML Code:
<if condition="in_array($threadinfo[forumid], $yourforums)">