Initializing a widget with a custom toolbar button

This is what I want to do

  CKEDITOR.plugins.add( 'groupwidget', {
    requires: 'widget',

    init: function( editor ) {
      CKEDITOR.dialog.add('GroupWidgetDialog', this.path + 'dialogs/groupwidget.js');
      editor.addCommand( 'GroupWidget', editor.execCommand('groupwidget') );

      editor.ui.addButton("GroupWidgetButton", {
        title: "Add Group",
        command: 'GroupWidget',
        icon: this.path + "icons/groupwidget.png"
      });


      editor.widgets.add('groupwidget', {
        dialog: 'GroupWidgetDialog'
      });
    }
  } );

Is it possible to use `addButton` to add a widget? This code doesn't work, but I was wondering if I am on the right track or if I'm walking closer and closer to the edge of a cliff.