I have managed to send additional parameters by setting them as the default for jQuery ajax. For example, at the bottom of the page where my validator is used:
<script type="text/javascript">
$.ajaxSetup({
beforeSend: function(xhr, settings) {
settings.url += "&id=" + $('#host').val();
}}
);
</script>
The jQuery documentation strongly advises against using the setup method in this manner, since it will affect any other ajax requests on the page. If your page is not too busy though, it may be a reasonable work around until something better becomes available in the Parsley library. Read more about it here, http://api.jquery.com/jQuery.ajaxSetup/