Help with using hook_form_alter on extra_options form

I am trying to integrate views with the OG Vocab module, and Im thinking the best way to do it is to add an extra option to the "Configure extra settings for filter Taxonomy: Term" form. So my code goes a bit like this...

  elseif($form_id == 'views_ui_config_item_extra_form')
  {
      $vocabularies = taxonomy_get_vocabularies();
      foreach ($vocabularies as $voc) {
        $options[$voc->vid] = check_plain($voc->name);
      }
    
      $options[]="Limit to vocabularies in current group"; 

      $form['vid']['#options']= $options;
  }

However nothing happens, even with increasing the weight of the og vocab module so it loads after views. I have no problem making a new form item appear:

  elseif($form_id == 'views_ui_config_item_extra_form')
  {
        
     $form['ogvocab'] = array(
      '#type' => 'checkbox',
      '#title' => t('Use only terms in current group'),
      '#default_value' => FALSE,
    );
	
  }

However, i have no idea how to pass the value of this into the 'value_form' form, which I'm also going to have to do a form_alter on. Any mention of the $this variable which the handler class uses causes an ajax meltdown.

Also, how do you guarantee it only appears in the 'Taxonomy:Term' extra options form?

thanks in advance for all help :)