virtual attribute

Hi,

We are using OpenLDAP as a frontend proxy for another LDAP server on the
backend. On the backend server, "displayname" attribute is not populated
but cn is populated. We like to fake out a virtual "displayname"
attribute on the frontend proxy OpenLDAP server, and the value of that
attribute needs to come from "cn" attribute.

Is there a way to do this? 
Any help is highly appricated.

Thanks,
Michael