NAML
visible_for_admins.naml

<override_macro name="visible_for_admins" parameters="selector">
    <n.put_in_head.>
        <n.array_of_user_ids var_name="site_admins" group="[n.administrators_group/]"/>
    </n.put_in_head.>
    <script type="text/javascript">
        $(document).ready(function() {
            if (Nabble.userId && site_admins.indexOf(Number(Nabble.userId)) >= 0)
                $('<n.selector/>').show();
        });
    </script>
</override_macro>