Installing Passenger when Nginx is already installed; Possible?

Rather a simple question I believe, is it possible to install passenger when nginx is already installed on your webserver?

If the answer is Yes, I already performed these actions:

At this very moment I already have nginx installed (for my PHP applications) and next I did a checkout of the passenger's git repository:

mkdir /repositories
cd /repositories/
git clone https://github.com/FooBarWidget/passenger.git
cd passenger/

and then add this snippet to /etc/nginx/conf/nginx.conf

  http {
      ...
      passenger_root /repositories/passenger;
      passenger_ruby /usr/local/rvm/wrappers/ruby-1.9.2-p290/ruby;
      ...
  }

However when I want to restart nginx I get the following error:

* Starting Web Server nginx
nginx: [emerg] unknown directive "passenger_root" in /etc/nginx/nginx.conf:19

Which concludes me to say that there is still some config I need to set, for nginx to be aware that we're using passenger.

My server block

server {
  listen 80;
  server_name rails.kreatude.com;
  root /srv/www/my_test_app;
  passenger_enabled on;
}