Hi,
as far as I know this is not possible with the current implementation of the portal. What you can try if that fit's your needs is to apply a filter as it is described here: http://blog.concurrency.com/infrastructure/service-manager-request-query-result-filtering
In short terms: An additional text field filters the picker - see details on the blog post about "Configure Query Results"
Peter Forster | MVP Virtual Machine 2002-2011 | Austria |