Geo Module. How to make nginx to check proxy for any ip?

[varan]

I mean I haven't got full list of ip addresses that can be proxy, so I want
nginx to look X-FORWARDED-FOR header for any ip address, and if the header
exists to determine geo using the header. If there's no X-Forwarded-For
header, then use ip address for geo.
is it acceptable to use "proxy 0.0.0.0/0" ?

for example:

geo $geo {
    default        ZZ;
    proxy          0.0.0.0/0;

    127.0.0.1/32   RU;
    192.168.0.1/32 UK;
    ... 
}

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,237392,237392#msg-237392