SILVERLIGHT 4 UserName Tracking

Question

  Hi,
 
  I have an application where I need to track the  user names. It is a Silverlight application developed using  Silverlight  4.0 using WCF services.

  IIS Settings are

   Authentication mode is ANONYMOUS
  WCF has been  used

I am aware that we can get this by using  WnodwsIdentity.GetCurrent or by using httpcontext.current.user.identity.name.  But for these two to work I need to set the authentication mode as windows in  IIS. This will basically disturb my application which is running live.  I know that it is not straight forward to use anonymous authentication and get  the user name , but what I am trying to see is that if there is any work so as  to not change the authentication to windows and get the user name then it would  really great. Do you guys have any idea how this can be accomplished (Any  workaround)? Is there anyway I can run a script and record the windows  username?
I tried using intiparams also --> it works fine from my local  when i connect through a smart card , but when i am in the orginial network  where the application it is repeatedly asking for username and password. Even on  entering correct username password it is not accepting.
Please give me light  on this stuff. Any help is appreciated.

Regards
Paulson C Paul