Nginx – Change Nginx document root from /usr/share/nginx to /etc/nginx

I've tried many things, STFW, RTFM but I still have this problem. The thing is:

I have a Nnginx installed in an AWS machine (other fella installed it, not me)
and I MUST serve several virtual hosts (*.conf files) which are being pulled from other server (production machine)

My main issue, is that the error handlers path in this .conf files are relatives, for example:

html/errores-prxy/handle404.html

as in

 location = /handle404.html {
     root html/errores-prxy;
}

The problem is that the document root path being called for this handler is /usr/share/nginx, as I can see in the error log:

2015/04/30 10:33:24 [error] 19542#0: *68 open() "/usr/share/nginx/html/errores-prxy/handle404.html" failed (2: No such file or directory), client: 77.240.116.140, server: www.abengoa.com, request: "GET / HTTP/1.1", upstream: "http://172.26.3.9:80/web/", host: "www.abengoa.es"

In this AWS machine, the Nginx is installed in /etc/nginx. And these handler files are in /etc/nginx/html/errores-prxy/handle404.html

So my question would be, how can I make Nginx look in /etc/nginx rather than in /usr/share/nginx/?

I could make a script to change the relative paths to absolute paths in all the *.conf but I'm seeking a more elegant solution as would be changing the Nginx document root.

Many thanks in advance.

Below is my nginx.conf (located in /etc/nginx/nginx.conf, just in case it helps)

user              nginx nginx;
worker_processes  2;
error_log       /var/log/nginx/error.log;
pid             /var/run/nginx.pid;

events {
                worker_connections  4096;
}

http {
                include         /etc/nginx/conf/mime.types;
                default_type    application/octet-stream;
                sendfile        on;
                gzip            on;
                gzip_comp_level 9;
                gzip_min_length 0;
                gzip_proxied    expired no-cache no-store private auth;
                gzip_types      text/plain text/css application/x-javascript application/xml application/javascript;
                set_real_ip_from        192.168.151.3;
                real_ip_header   X-Forwarded-For;
                proxy_set_header   Host             $host;
                proxy_set_header   X-Real-IP        $remote_addr;
                proxy_set_header   X-Forwarded-For  $proxy_add_x_forwarded_for;
                proxy_intercept_errors on;
                log_format main '$remote_addr - $remote_user [$time_local] '
                        '"$request" $status $body_bytes_sent "$http_referer" '
                        '"$http_user_agent"' ;
                access_log      /var/log/nginx/access.log main;

                client_max_body_size            50m;
                client_body_buffer_size         4k;
                client_header_buffer_size       2k;
                keepalive_timeout               5 5;
                client_body_timeout             10;
                client_header_timeout           10;
                send_timeout                    10;
                proxy_connect_timeout           5;
                proxy_send_timeout              20;
                proxy_read_timeout              120;
                proxy_buffer_size               8k;
                proxy_buffers                   8 32k;
                proxy_busy_buffers_size         32k;
                proxy_temp_file_write_size      32k;
                server_names_hash_bucket_size   128;
                server_names_hash_max_size      1280;
                server_name_in_redirect         off;
                proxy_cache_path  /etc/nginx/cache  levels=1:2   keys_zone=prxy-cache:100m max_size=256m;
                proxy_cache_key   "$scheme$host$request_uri";
                include /etc/nginx/conf/*.conf;
                include /etc/nginx/conf/sites-enables/*.conf;
}