reply to comment excerpt instead of author in comment title

Finally I found a way and I am posting it here to address any further requests for such a workaround.

You may add a customized version of comment_form_title function to your theme’s functions.php file and call it in your theme’s comments.php file.

function my_comment_form_title( $linktoparent = true ){
    global $comment;
    $noreplytext = __( 'Leave a Reply' );
    $replytext = __( 'Leave a Reply to %s' );
    $replytoid = isset($_GET['replytocom']) ? (int) $_GET['replytocom'] : 0;
    if( 0 == $replytoid ){
        echo $noreplytext;
    }else{
        $comment = get_comment( $replytoid );
        $excerpt = get_comment_excerpt( $replytoid );
        $title = ( $linktoparent ) ? '<a href="#comment-' . get_comment_ID() . '">' . $excerpt . '</a>' : $excerpt;
        printf( $replytext, $title );
    }
}