WordPress: add tinymce editor to the wordpress excerpt field

excerpt_tinymce.php

function tinymce_excerpt_js(){ ?>
        <script type="text/javascript">
                jQuery(document).ready( tinymce_excerpt );
                    function tinymce_excerpt() {
                        jQuery("#excerpt").addClass("mceEditor");
                        tinyMCE.execCommand("mceAddControl", false, "excerpt");
                        tinyMCE.onAddEditor.add(function(mgr,ed) {
                            if(ed.id=="excerpt"){
                                ed.settings.theme_advanced_buttons2 ="";
                                ed.settings.theme_advanced_buttons1 = "bold,italic,underline,seperator,justifyleft,justifycenter,justifyright,separator,link,unlink,seperator,pastetext,pasteword,removeformat,seperator,undo,redo,seperator,spellchecker,";
                            }
                        });
                    }
        </script>
    <?php }
    add_action( 'admin_head-post.php', 'tinymce_excerpt_js');
    add_action( 'admin_head-post-new.php', 'tinymce_excerpt_js');
    function tinymce_css(){ ?>
        <style type='text/css'>
                    #postexcerpt .inside{margin:0;padding:0;background:#fff;}
                    #postexcerpt .inside p{padding:0px 0px 5px 10px;}
                    #postexcerpt #excerpteditorcontainer { border-style: solid; padding: 0; }
        </style>
    <?php }
    add_action( 'admin_head-post.php', 'tinymce_css');
    add_action( 'admin_head-post-new.php', 'tinymce_css');
 
    function prepareExcerptForEdit($e){
        return nl2br($e);
    }
    add_action( 'excerpt_edit_pre','prepareExcerptForEdit');