ckfinder own plugin with dialog and wysiwyg textarea

hello,

i hope anyone can help me. how i can create in a own ckfinder plugin a dialog with a wysiwyg textarea element?

i have try this directly with

contents : [
                       {
                            id : 'tabFileDescription',
                           label : '',
                           title : api.lang.filedescription.title,
                           expand : false,
                           padding : 0,
                           elements :
                           [
                                {
                                    type : 'text',
                                    id : 'fileDescriptionTitleId',
                                    label: api.lang.filedescription.headline
                                },
                               {
                                   type : 'textarea',
                                   id : 'fileDescriptionTextId',
                                   name : 'fileDescriptionTextId',
                                    className : 'jquery_ckeditor',
                                    label: api.lang.filedescription.description,
                                   rows : 10,
                                   cols : 40,
                                    onShow : function() {
                                        var element = this;
                                        doc = element.getElement().getDocument();
                                        var win = doc.getWindow();

                                        var head= doc.$.getElementsByTagName( 'head' )[0];
                                        var script= doc.$.createElement( 'script' );
                                        script.type= 'text/javascript';
                                        script.src = '/admin/js/ckeditor/ckeditor.js';
                                        head.appendChild( script );

                                        var editor = CKEDITOR.replace( '31_textarea' );
                                    }
                               }
                           ]
                       }
                   ],

but this is not correct. (31_textarea is the textarea element ID in html)

michael