Searching through other sites users

Hi all,
the scenario i have to deal with is the following: each unit has each own jabber server (ejabberd in new installation) and there is someone who handles local user registration.
I want to have a central ejabberd server that will be able to "proxy" connections to other users of other units. Basically if i want to list all users of all units i can search just the central node.

i.e.
Unit1 (user11@unit1.tld, user12@unit1.tld)
Unit2 (user21@unit2.tld, user22@unit2.tld)
Central (admin@central.tld)

so user11@unit1.tld doing a discovery on central.tld will be able to know about user12@unit1.tld, user21@unit2.tld and user22@unit2.tld

is this possible?

i did try the following:
in the ejabberd.cfg i added
mod_disco[{extra_domains,["unit1.tld","unit2.tld"]}]

and i can browse a bit of info (i tried with tkabber client) but when i try to access the node "all users" i get a 403 error

thank everybody :)