Multiple Instances with Director

[Cassidy Larson]

I have four front end servers with two backend servers.
Each front end server has three instances for different mail hosts
(individual SSL certs, etc).

I'm looking at adding a fourth instance on each front end server for the
director process.

Currently we just return the backend server ip via SQL and use the old
master username/password to proxy the inbound POP/IMAP sessions to the
correct backend server.
The plan is for each instance to have connect to the same list of
director_servers (one from each front end server).

What's the trick to separate a director instance into its own setup and
having multiple instances/servers connect to that director?

Currently I have on my proxy instance:

director_servers = 10.128.1.42:9090      (this is the inet_listener from
the director instance)
service director {
  unix_listener login/director {
    mode = 0666
  }
  fifo_listener login/proxy-notify {
    mode = 0600
    user = $default_login_user
  }
  unix_listener director-userdb {
    mode = 0600
  }
}

And I get in logs:
director: Fatal: No inet_listeners defined for director service (for
standalone keep director_servers empty)

Do I need an inet_listener on the front end instance if I want to forward
all director queries to the director_servers list?

Or is there some other trick to get a proxy front end to talk to a separate
director instance(s)?

Thanks,

Cassidy