How to pass custom parameters to PHP from Nginx?

You can pass additional parameters via fastcgi_param directive. I'm sure because I used this funcionality.

My exemplary nginx config

server {
    server_name localhost;
    include     conf/defaults.conf;
    root        /var/www;

    location    ~* "\.php$" {
        fastcgi_param CRS "crs";
        include conf/fastcgi-php.conf;
    }                                           
}

And part of phpinfo() output:

...
_SERVER["USER"] fcgi
_SERVER["HOME"] /dev/null
_SERVER["FCGI_ROLE"]    RESPONDER
_SERVER["REMOTE_USER"]  no value
_SERVER["CRS"]  crs
_SERVER["QUERY_STRING"] no value