Madhu,
My takeaway from Note is that SAP does not provide this functionality until 10.1 release. In our case, our source of user details is the Active Directory, and all users have managers there, so failure to enforce mandatory validation of that field has not been an issue.
Yours is a question for SAP, not this Community, but I would expect them to say that you need to upgrade to 10.1, which is probably not what you wanted to hear. but think of it this way: sooner or later, one of your connected systems is likely to upgrade to a NetWeaver release forcing an upgrade of GRC. Since this is a pain point, you might want to just bite the bullet and upgrade now.
Gretchen