I think no, because in this case plugin will be not loaded... But we can go by another way... It is not fully correct (because it will make SQL-query to get comments list but will not show it for guests).
1. Open /components/com_jcomments/tpl/default/tpl_index.php
2. Find code:
$comments = $this->getVar('comments-list', '');
and add after:
$user = JFactory::getUser();
if (!$user->id) {
$comments = '<div class="comments-list" id="comments-list-0">'. JText::_('You need login to view or make a comment') .'</div>';
}