Você pode resolver isso usando gatilhos de manutenção baseados em IP
Experimente o seguinte na parte inferior da página: link
You could just do it like this in the global section:
geo $maintenance { default 0;
80.15x.yy.zz/29 0; # your IPs still allowed
80.15x.yy.zz/29 0; # another bunch of allowed IPs }
and in the server section add this:
if ($maintenance) { rewrite ^(.*)$
/yourmaintenancefile.html last; }
When you want to start maintenance just switch the "default 0;" to "default 1;" in the $maintenance block and reload your nginx.
Have a look at http://wiki.nginx.org/NginxHttpGeoModule