<style>
a.addthis_button span, a.addthis_button strong { display:none; }
</style>

<!-- ADDTHIS BUTTON BEGIN -->
<script type="text/javascript">
var addthis_config = {
     pubid: "YOUR-PROFILE-ID"
}
</script>

<a href="http://www.addthis.com/bookmark.php?v=250" 
        class="addthis_button"><span>Menu appears at page top</span></a>
<a href="http://www.addthis.com/bookmark.php?v=250" 
        class="addthis_button"><strong>Menu appears next to link</strong></a>

<script type="text/javascript" src="http://s7.addthis.com/js/250/addthis_widget.js"></script>
<!-- ADDTHIS BUTTON END -->

http://www.addthis.com/help/default-code

If you use hidden text spans inside link buttons instead of an image tag, addthis menus seem to attach to the page top instead of the link. For some reason a strong tag used the same way works.

Fix for Addthis menu appearing at page top

HTML