You're not going to be able to restrict this on the SQL Server side, so far as I am aware. However, you can set up an IPSec policy that could block in-bound traffic on the 5 IP addresses for the SQL Server port.
K. Brian Kelley
http://www.truthsolutions.com/
Author: Start to Finish Guide to SQL Server Performance Monitoring
http://www.netimpress.com/
K. Brian Kelley
@kbriankelley