Change "Comments On:" channel title in RSS feeds

Is there a way to change the “Comments On:” RSS channel title in the comments RSS feed without hacking the core files? I’ve tried the following:

function mytheme_rss_title($title) {
	$mytitle = "Test Title";
	return $mytitle;
}
add_filter('the_title_rss', 'mytheme_rss_title');

However this changes only the text after the “Comments On:.” I’ve tracked the text to line 22 of \wp-includes\feed.php but it doesnt look like I have any options other than editing that file. I have also searched for plugins for this, all of which only modify the code after “Comments On:.”

Thanks in advance for any reply.