User Role check? Forcing visitors into roles for intranet schema

I am trying to force anonymous uses into roles by doing something like this:

$GLOBALS['user']->roles[sizeof($GLOBALS['user']->roles)+2] = "anonymous KNOWN IP";

However it seems that nodeaccess doesn't lookup the $GLOBALS['user'] array. Do I need to force a visitor into a "User" account and not just a role?

I am forcing the user into a role only if they have an ip address within a certain range (an intranet schema).