Seeking for dynamic proxy_pass solution

[autogun]

Hello,

I'd like to achieve something as follow using nginx -

When browsing to http://myserver/10.10.21.102 for example,
I want proxy_pass to be set to http://10.10.21.102;

Im getting somewhere but still need help,
Catching the argument this way -
http://server/?device=10.10.21.102

In nginx config -
set $ip $arg_device;
proxy_pass  http://$ip;

Which actually works but breaks when there's an image/css/js, for example -
[09/Mar/2014:23:05:44 +0200] "GET /?device=10.10.21.102 HTTP/1.1" 200 689
"-" "Mozilla/4.0 ...
[09/Mar/2014:22:58:30 +0200] "GET /welcome.png HTTP/1.1" 500 594
"http://server/?device=10.10.21.102" "Mozilla/4.0 ...

When I try to access http://server/?device=10.10.21.102/welcome.png - It
works.

What would be the easiest way to solve this so css,js,images will be called
as:
GET /?device=10.10.21.102/welcome.png
and not just 
GET /welcome.png

Thank you,
D

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,248258,248258#msg-248258