Add a global preference to disallow registration!

I'm deploying XWiki in an environment that requires strict security.
Out of the box XWiki does provide me with everything i need to properly secure the system, except for one thing!

I need to modify templates/header.vm to get rid of the register option, since access to my XWiki is invitation only.

Can a global preference be added to allow or disallow users to register themselves, if disallowed the register option should be shown in the header.