Dynamic proxy_pass hosts

[Igor Katson]

In Apache it is possible to dynamically alter the proxy_pass remote 
host, i.e. like this

RewriteRule ^/proxy_everything/(.*)$ http://$1 [P]

So I cant extract the host from the URI, or from the environment 
variable etc.

Is it possible to do the same with nginx?

Thanks in advance,
Igor Katson.