Seems I found more easier solution...
1. Open file /plugins/content/jcomments.php
2. Find code:
$config->set('comments_on', intval($commentsEnabled));
$config->set('comments_off', intval($commentsDisabled));
$config->set('comments_locked', intval($commentsLocked));
and add after next code:
if ($article->id == 123 || $article->id == 124) {
$user = & JFactory::getUser();
if ($user->usertype != 'Super Administrator' && $user->usertype != 'Administrator') {
$config->set('comments_off', 1);
}
}
This code will disable commeting for articles with ID 123 and 124 for all usergroups except Administrators and Super Administrators. Hope it help you...