[nerbert]

<label for="bccpmrecips_ctrl" class="full">{vb:rawphrase bcc}:</label>
<div id="bccpmrecips" class="popupmenu nomouseover noclick nohovermenu">
        <input type="text" class="primary full textbox popupctrl" id="bccpmrecips_ctrl" name="bccrecipients" />
</div>
<script type="text/javascript" src="clientscript/vbulletin_ajax_suggest.js?v={vb:raw vboptions.simpleversion}"></script>
<script type="text/javascript">
<!--
        bccrecip_sugg = new vB_AJAX_NameSuggest('bccrecip_sugg', 'bccpmrecips_ctrl', 'bccpmrecips');
        //bccrecip_sugg.allow_multiple = true; 
//-->
</script>

I think this will do it. I got this out of the PM page template and modified it a bit. you can change those element id's, just observe how they match up with params in the JS function. I doubt you want multiple names so I commented out that part