GianClaudio,
You can use Extended ACL and notes.ini parameter NTS_LOOKUP_ENFORCE_ACL=1 to work this around.
On the Target Field of xACL, Please select the Domain that you want users to be restricted to look up to. (It should be specified in the secondary directory). After that click the "Add" button on the Access List field on what groups and/or specific users are prohibited to access that domain. After that, set the Attributes field of your choice. I recommend that you "Deny" all of the attributes.
Better yet open a PMR if you need a more detailed explanation with this. Hope it helps!