How to configure nginx + Unicorn to avoid timeout errors?

How to configure nginx + Unicorn to avoid timeout errors?

I have a Rails (v3.2.13, Ruby 2.0.0) application running on nginx +
Unicorn (Ubuntu 12.04). All is working well, except when an admin user is
uploading users (thousands) via a CVS file. The problem is that I have set
timeout to 30 seconds and the import process takes much more time. So,
after 30 seconds I get an nginx 502 Bad Gateway page (Unicorn worker is
killed).
The obvious solution is to increase timeout, but I don't want this because
it'll cause another problems (I guess), because it's not a typical
behavior.
Is there a way to handle this kind of problems?
Thanks a lot in advance.
PS: Maybe a solutions is to modify the code. If so, I want to avoid the
user to perform another request.
nginx-app.conf
upstream xxx {
server unix:/tmp/xxx.socket fail_timeout=0;
}
server {
listen 80;
...
location / {
proxy_pass http://xxx;
proxy_redirect off;
...
proxy_connect_timeout 360;
proxy_send_timeout 360;
proxy_read_timeout 360;
}
}
unicorn.rb
worker_processes 2
listen "/tmp/xxx.socket"
timeout 30
pid "/tmp/unicorn.xxx.pid"