Hi,
Just realized that you asked about a field, not a meta box. The include / exclude extension works for meta boxes only, not for fields.
So, in this situation, you probably need to use PHP code to check and register a field for a meta box. Something like:
$fields = array(); // Define all your fields here
if ( current_user_can( 'manage_options' ) ) {
$fields[] = array(
'type' => 'text',
'name' => 'Custom field for admin only',
'id' => 'admin_only',
);
}
// Register meta box
$meta_boxes[] = array(
'type' => 'user',
'title' => 'Profile fields',
'fields' => $fields,
);