Hi pehansen,
You can add him like any other agent. Do a search for him on the regular search page, then check the "Add to Query List" box.
Also, on the private listings page is a link to the right of his name that says "View Profile". That will take you to the agent's profile page and you can add him to your query list by checking the box there.
I hope that helps. If not, or you have any other questions, please let me know.