Ok, I finally found it. You can use the format_date function; the documentation is a little sparse. My syntax looks like this:
<?xdoxslt:format_date($p_Date, 'MMM yyyy','MM-dd-yyyy', $_XDOLOCALE, $_XDOTIMEZONE)?>
The first parameter is the target format, the second is the input mask. The second can be overridden to use a specific l18n style.