class Page extends SiteTree {

public static $has_one = array(
   'SidebarWidgets' => 'WidgetArea'
);

function getCMSFields() {
   $fields = parent::getCMSFields();

   $fields->addFieldToTab('Root.Content.Widgets', new WidgetAreaEditor('SidebarWidgets'));
   
   return $fields;
}

}

class BlogHolderDecorator extends DataObjectDecorator {
   
   public function getCMSFields() {
    $fields = parent::getCMSFields();
    $this->extend('updateCMSFields', $fields);
    return $fields;
   }
   
   public function updateCMSFields(FieldSet $fields) {
      $fields->removeByName('SideBar');
      
      return $fields;
   }

}

DataObject::add_extension('BlogHolder', 'BlogHolderDecorator');