The final solution with programming do not exist. A way to solve your issue is to hack article.php and test if user is an anonymous. For exemple:
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if ($A['count'] > 0 && !COM_isAnonUser()) {
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if( !empty( $bodytext ) && !COM_isAnonUser())
{
$article->set_var( 'lang_readmore', $LANG01[2] );
$article->set_var( 'lang_readmore_words', $LANG01[62] );
$numwords = COM_numberFormat(count(explode(' ', COM_getTextContent($bodytext))));
$article->set_var( 'readmore_words', $numwords );
$article->set_var( 'readmore_link',
COM_createLink(
$LANG01[2],
$articleUrl,
array('class'=>'story-read-more-link')
)
. ' (' . $numwords . ' ' . $LANG01[62] . ') ' );
$article->set_var('start_readmore_anchortag', '<a href="'
. $articleUrl . '" class="story-read-more-link">');
$article->set_var('end_readmore_anchortag', '</a>');
$article->set_var('read_more_class', 'class="story-read-more-link"');
} else if ( !empty( $bodytext ) ) {
$article->set_var( 'lang_readmore', 'Login to read more');
$article->set_var( 'lang_readmore_words', 'Login to read more' );
$numwords = COM_numberFormat(count(explode(' ', COM_getTextContent($bodytext))));
$article->set_var( 'readmore_words', $numwords );
$article->set_var( 'readmore_link',
COM_createLink(
$LANG01[2],
$_CONF['site_url'] . '/users.php',
array('class'=>'story-read-more-link')
)
. ' (' . $numwords . ' ' . $LANG01[62] . ') ' );
$article->set_var('start_readmore_anchortag', '<a href="'
. $_CONF['site_url'] . '/users.php" class="story-read-more-link">');
$article->set_var('end_readmore_anchortag', '</a>');
$article->set_var('read_more_class', 'class="story-read-more-link"');
}