AddThis

Addthis - aync loading for facebook and twitter button

I have started loading addthis script using following code

<script type="text/javascript">
(function() {
var at = document.createElement('script');

at.type = 'text/javascript';

at.async = true;
at.src = ('https:' == document.location.protocol ? 'https://' : 'http://')

+ 's7.addthis.com/js/250/addthis_widget.js#pubid=pub-id';
var sat = document.getElementsByTagName('script')[0];

sat.parentNode.insertBefore(at, sat);
})();
</script>

But now I still have a problem. Facebook and Twitter are still loading synchronously coz there code is hard coded in addthis script to load as synchronously. Is there any work around to resolve this issue.