Multiples proxy for 1 servername

[ceooph]

Hi all,

We do reverse proxy to access from internet to some documentation 
filtering by ip address. These documentations are hosted on commercials 
portals.
For 1 base we are often redirect between 2 or 3 (sometimes 6) servers. 
(www.exemple.com -> secure1.exemple.com -> secure2.exemple.com -> 
auth.exemple.com -> go.exemple.com -> www.exemple.com)
And we have access to more than 50 bases !
Do you know if with nginx it's possible to do proxy_pass (and 
proxy_redirect) to these server one 1 virtual name ?

I want to write something like this

base1.mydomain.com
proxy_ www.exemple.com
proxy_ secure1.exemple.com
....

base2.mydomain.com
proxy_ www.exemple2.com
....

I try it with different location for each server but it's doesn't work.

Thanks in advance for your help.