load balancing - nginx geo location module configuration using geo database?

I've setup nginx as a reverse proxy for a couple of apache
backend/upstream servers.

Using the href="http://dev.maxmind.com/geoip/legacy/geolite/" rel="nofollow noreferrer">GeoLite
database from MaxMind, I'm trying to loadbalance requests between the two
servers dependent on the clients country
code.

Nginx
Configuration:

geo $geo
            {
 default default;
 include geo.conf;
 }

            upstream default.backend {
 server 192.168.0.1:8080; #Server A

            server 192.168.0.2:8080; #Server B

 }
 upstream
            DE.backend {
 server 192.168.0.1:8080; #Server A
 }

            upstream US.backend {
 server 192.168.0.2:8080; #Server B

            }
server {
 listen 80;
 server_name
            myserver.com;

 location / {
 proxy_pass
            http://$geo.backend;
 proxy_set_header Host $host;
 proxy_set_header
            X-Real-IP $remote_addr;
 proxy_set_header X-Forwarded-For
            $proxy_add_x_forwarded_for;

            }

So I'm trying to
send any German clients to server A, and US clients to server B, and any other clients
not matching German or US country codes to be loadbalanced between servers A &
B.

However, since
geo.conf contains country codes for many (all) other countries,
these values are being set to the variable $geo, as opposed to
the 'default'
value.

With my current configuration this causes
'502 Bad Gateway' errors with all requests that aren't DE or
US.

Nginx error
log:

2013/10/11 08:18:50 [error]
            25017#0: *1 no resolver defined to resolve NL.backend, client: 85.17.131.209, server:
            myserver.com, request: "GET / HTTP/1.1", host:
            "myserver.com"

Nginx
access
log:

85.17.131.209 - -
            [11/Oct/2013:08:18:50 -0700] "GET / HTTP/1.1" 502 574 "-" "Mozilla/5.0 (X11; Linux
            x86_64) AppleWebKit/537.31 (KHTML, like Gecko) Chrome/26.0.1410.63 Safari/537.31"
            "-"

How can I
configure nginx.conf to interpret any IP country code value
from geo.conf that's not DE or US as
default, and loadbalance it accordingly to upstream
default.backend?