For any MODX users out there, it looks like this:
<script type="text/javascript">Mibew.ChatPopup.init({
"id":"<unique button code>",
"url":"http:\/\/domain.com\/mibew\/index.php\/chat?locale=en&name=[[+modx.user.id:userinfo=`username`]]&email=[[+modx.user.id:userinfo=`email`]]",
...
</script>