I think I need something like this: http://stackoverflow.com/questions/18452676/dynamic-proxy-pass-with-map-and-regexp

but the difference is that in my case I need to split in 2 parts, the server name, "aserverthatlistens.com" ($some_url) and then the rest of the args: "serviceToCall" ($some_args) (which could be even longer). So then I think that I should do something like:

location ~ ^ xxxx {
resolver 8.8.8.8;
add_header Access-Control-Allow-Origin "*";
proxy_pass http://$some_url$some_args$args;
proxy_redirect off;
access_log on;
}

but the problem is how to get both parts and make the correct calles.... (xxxx part and proxy_pass call)

Thanks in advance,