//Create your sharelet with desired properties and set button element to false
var object = SHARETHIS.addEntry({
title:'Arge Kanzleimanagement im DAV',
summary: 'Seite weiterempfehlen'},
{button:false, onmouseover:false});
//Output your customized button
document.write('<span id="share"><a href="javascript:void(0);"><div id="stLeft"><img src="fileadmin/template/res/img/sharethis.png" /></div><div id="stRight"><img src="fileadmin/template/res/img/sharethisHead.png" /><br>Schnell weitersagen.</div></a></span>');
//Tie customized button to ShareThis button functionality.
var element = document.getElementById("share");
object.attachButton(element);