Display custom text if there is no comments
In your node.tpl.php you could check the $comment_count variable to see if there are comments. If so, render the comments, if not display your alternet text.

Example:

&lt;?php if ($comment_count &gt; 0 ): ?&gt;
  &lt;?php print render($content['comments']); ?&gt;
&lt;?php else: ?&gt;
        &lt;strong&gt; 0 comments yet&lt;/strong&gt;
        &lt;?php echo l('Be the first','commentpath'); ?&gt;
&lt;?php endif; ?&gt;