Our website currently runs wordpress to manage the front end site www.example.com

When users register they get a subdomain username.example.com where they can login to our application. The application is built on zend framework. I'd like to have the zf project on an entirely different server than where we run the wordpress www.example.com domain.

How would the default server config be setup since the front end site is on another server with different IP? Virtual hosts would be setup as usual, i'm just not sure how to configure the main server so it redirects to www.example.com? Any help is appreciated

Thanks