Active Subscriber allows you to override the server used to query the Active Directory Service.
This is done via a registry setting (all the usual disclaimers about editing your registry apply!)
Run regedit.exe and open HKEY_LOCAL_MACHINE and navigate to the
Add a new String Value, "Domain Controller" and set it to the (fully qualified) hostname of the machine you wish to use for Active Directory queries. This should be a server which contains a writeable replica (or master copy) of the complete Active Directory site containing your Active Subscriber Data OU.