If you're using the same plugin structure as the Joomla User plugin and just loading a different XML file, what I suggested above should work.
For more information on how to create or customize your own Profile plugin, see
Joomla's Profile Plugin documentation
. If you've made larger changes to the profile plugin code, you may need to update our plugin more, but the main things to do are listed above: Look for the correct plugin and load the correct XML file for the fields to display.
I hope that helps,
Alex