Perhaps this plugin can help: http://wordpress.org/extend/plugins/extended-super-admins/ in combination with hard-coding the global variable, $super_admins, specific to each site.
It should be able to be set in a hook as the site admin menu is loaded -- not quite sure how to enforce that yet. It seems a promising solution to an issue I'll have to deal with myself, shortly.
See: http://svn.automattic.com/wordpress/trunk/wp-admin/includes/ms.php and note the return if the global, $super_admins is already set.
/**
* Grants super admin privileges.
*
* @since 3.0.0
* @param int $user_id
*/
function grant_super_admin( $user_id ) {
global $super_admins;
// If global super_admins override is defined, there is nothing to do here.
if ( isset($super_admins) )
return false;
do_action( 'grant_super_admin', $user_id );
// Directly fetch site_admins instead of using get_super_admins()
$super_admins = get_site_option( 'site_admins', array( 'admin' ) );
$user = new WP_User( $user_id );
if ( ! in_array( $user->user_login, $super_admins ) ) {
$super_admins[] = $user->user_login;
update_site_option( 'site_admins' , $super_admins );
do_action( 'granted_super_admin', $user_id );
return true;
}
return false;
}
/**
* Revokes super admin privileges.
*
* @since 3.0.0
* @param int $user_id
*/
function revoke_super_admin( $user_id ) {
global $super_admins;
// If global super_admins override is defined, there is nothing to do here.
if ( isset($super_admins) )
return false;
do_action( 'revoke_super_admin', $user_id );
// Directly fetch site_admins instead of using get_super_admins()
$super_admins = get_site_option( 'site_admins', array( 'admin' ) );
$user = new WP_User( $user_id );
if ( $user->user_email != get_site_option( 'admin_email' ) ) {
if ( false !== ( $key = array_search( $user->user_login, $super_admins ) ) ) {
unset( $super_admins[$key] );
update_site_option( 'site_admins', $super_admins );
do_action( 'revoked_super_admin', $user_id );
return true;
}
}
return false;
}