Hi Jared,
I have to guess by your comments that you did not bother to even try my suggestion?
Having done some further digging through a clean install I find that the displayHead() is referenced in the libraries/gantry/core/gantry.class.php file. It is shown as this...
public function displayHead()
{
if (defined('GANTRY_FINALIZED')) return;
//stuff to output that is needed by joomla
echo '<jdoc:include type="head" />';
}
Based on that you could still use the code suggested by the Joomla link you provided but place it before the gantry call and exclude the <jdoc:include type="head" />
Hope this helps