The right way to add auxiliary classes

[dan@docmail.docisp.com]

What's the right way to add auxiliary classes?
I am going to use 'organizationalPerson' object class that's shipped
with OpenLDAP, but need to store additional information, like 'givenname'
that's absent from that class. I createad a separate blah.oc.conf for my
purposes that should be auxiliary to 'organizationalPerson'. If I'd like
to create an entry in the database like rid=blah,dc=ldap,dc=domain,dc=com,
what should be specified for it's 'objectclass' attribute if 
that entry should contain attributes from both blah and organizational person?
Is the following correct? Since OpenLDAP does not distinguish between object
class types, what's the most optimal way to create entries for easier migration
to LDAP V.3 server in the future?

objectclass: person
objectclass: organizationalperson
objectclass: blah

Also do I need to merge organizationalPerson definition with blah definition
for best migration path to LDAP V.3? 

Thank you very much.