You should add the list of comments within the comments.php file the following code:
<iframe src="http://www.facebook.com/plugins/like.php?href=<?php echo urlencode(post_permalink() . '#comment-' . comment_ID()); ?>&layout=standard&show_faces=false&width=450&action=like&colorscheme=light" scrolling="no" frameborder="0" allowTransparency="true" style="border:none; overflow:hidden; width:450px; height:60px;"></iframe>
And then customize the display rules in the stylesheet. Hope that helps. 😉