Excluding Access to some domains in multisite

hi,

we have 200+ domains in multi-site. we want only the admin to have access to 20 of these.

one answer was to do 2 separate installs, giving the admin exclusive access to the 2nd install. the problem here is that the admin needs to use the global posts plugin to feed recent posts from the main install to the exclusive install domains. for example:

domains 1-180 are accessible to all
domains 181-200 accessible only to admin

key: admin wants domains 181-200 to list recent posts from all 200 domains.

can we give the 2nd install global post access to the first?

or is there a way to exclude users from accessing certain domains on a single install?

thanx!!!