Ok, I think I have found a solution.  I wanted to check here to make sure I am not going to do any damage though.
If i goto "domains" in the control panel and "add domain"  I can enter the domain name that the employee should not be visiting and point it to the primary site and then tell it to resolve locally.  I tested this with 
www.cnn.com and it immediatly came back the "This web site is under construction" since i have not setup the primary website.  
Is this ok to do?  are there any problems that i will run into by doing this with numerous sites that we dont want the employees visiting?
Thanks.
Andy