Make addthis_bubble_style available in Basic Toolbox

Any progress?

Try the following, works for me. Had no time to build a patch.
in addthis.displays.addthis.inc line number 37 change this:

    $items[$service] = array(
      '#theme' => 'addthis_element',
      '#tag' => 'a',
      '#value' => '',
      '#attributes' => array(
        'href' => $addthis->getBaseBookmarkUrl(),
        'class' => array(
          'addthis_button_' . $service,
        ),
      ),
      '#addthis_service' => $service,
    );

into this:

    $items[$service] = array(
      '#theme' => 'addthis_element',
      '#tag' => 'a',
      '#value' => '',
      '#attributes' => array(
        'href' => $addthis->getBaseBookmarkUrl(),
        'class' => array(
          'addthis_button_' . $service,
        ),
      ),
      '#addthis_service' => $service,
    );

	$addthis_counter = array(
	  '#theme' => 'addthis_element',
	  '#tag' => 'a',
	  '#value' => '',
	  '#attributes' => array(
		'href' => '',
		'class' => array(
		  'addthis_counter addthis_bubble_style',
		),
	  ),
	);
	
	if($service == 'addthis') {
	  array_push($items, $addthis_counter);
	}

Even better, as of version 7.x-4.x you can use use HOOK__addthis_markup_alter to this. See example below:

function YOURMODULE_addthis_markup_alter(&$markup) {
  if (isset($markup['addthis'])) {
	$markup['counter'] = array(
	  '#theme' => 'addthis_element',
	  '#tag' => 'a',
	  '#value' => '',
	  '#attributes' => array(
		'class' => array('addthis_counter', 'addthis_bubble_style'),
	  ),
	);
  }
}