Probably not. If you have a corresponding $has_many and $has_one, you shouldn't need any of that. Maybe the sourceID() call.. cause I know SiteConfig is a bit of a different animal.

The solution offered in this topic works for me, but somehow not totally:

In my customsiteconfig.php i have this code:
$manager = new DataObjectManager(
   $this->owner,
   'Quotes',
   'Quote',
   array(            
      'Quote' => 'Quote'            
   ),
   'getCMSFields_forPopup'         
);
$manager->setSourceID($this->owner->ID);
$manager->setParentClass('SiteConfig');
$fields->addFieldToTab("Root.Quotes",$manager);

Then, in my Quote.php i have:

class Quote extends DataObject
{
   static $db = array (      
      'Quote' => 'HTMLText'      
   );

   static $has_one = array (      
      'SiteConfig' => 'SiteConfig'
   );   

   public function getCMSFields_forPopup()
   {
      return new FieldSet(         
         new SimpleHTMLEditorField('Quote','Quote')         
      );
   }
}

I use this on a multilanguage site, so in my _config.php i have:
Object::add_extension('SiteConfig', 'Translatable');

At first, the dataobjectmanager loads the items for the language that has been selected. When I click the "add quote" button and click away or save, the dataobjectmanager loads the items for the default language. Somehow, it loses the reference to the loaded siteconfig. Does anyone else have troubles with DOM in CustomSiteConfig with multiple languages?

I'm currently having a battle with SiteConfig ...

FYI: I found that I had to do what Juanitou did and also add "$manager->setSourceID($this->owner->ID);" to get a complete solution: add items, retrieve component set.

Without the setSourceID() call, any query on a 'has_many' set (i.e. SiteConfig::current_site_config()->MyHasManyItems()) would return an empty ComponentSet; even though in the CMS I could see all the items.

J.