Searching few domains for one uid

[kefast@o2.pl]

Hello,
I've got 3 domains (departments), for egzample:

a.com
b.com.de
c.com.fr

and each of them has it's own
posixAccount users (moved from nis).
I want every user in each department to be albe to login with his
credencials, localized under people.$(domainname) to machines under
all domains, but as far as I know, You cant search for uid or anyting else in more then one
domain, cause a BASE attrib in ldap.conf accept only one search base.
Is the only way to do this is change the schema to:
a.com.corp
b.com.de.corp
c.com.fr.corp
and set the search base to dc=corp ?
I've also read about setting base to config and put it there.

-- 
Pozdrowienia,
 kefast@o2.pl