Hi,

some time ago I had a similar issue and I grab some parts of nginx internals modules and did one specific to me.
My issue was to use the first XForwardedFor IP, but only when the client address was the Google Chrome Proxy.
I don't know if this is the best approach,
but I check the client ip using the reverse dns and, if the ip came from Google,
I change it for the first ip on XFowardedFor header.
Doing that, the GeoIP module can be executed with the "real ip" instead of the Google.

If you want to look how I did, the code is here https://github.com/wandenberg/nginx-trusted-proxy-resolver-module.
(The idea is to expand this module to support other mobiles proxies like Windows Phone and Mini Opera.)

Regards,
Wandenberg