Server Side sort and the cn attribute

[Edward Capriolo <edlinuxguru@gmail.com>]

We use openldap as a back end for many things. One of the thing, it
can be used for is an address book for outlook. Recently we upgrade to
2.4.16->2.4.20 from 2.(who knows how old).

Outlook 2003 clients stopped working:

http://support.microsoft.com/kb/555536

So I followed the instructions here to enable server side sorting:

http://bacedifo.blogspot.com/2009/09/server-side-sort-with-openldap2418.html

I was able to add the ordering to the sn attribute.

attributetype ( 2.5.4.4 NAME ( 'sn' 'surname' )
     DESC 'RFC2256: last (family) name(s) for which the entity is known by'
     ORDERING caseIgnoreOrderingMatch
     SUP name )

Unfortunately outlook is looking at the cn attribute

@400000004b21316a0e808064 sssvlv: no ordering rule specified and no
default ordering rule for attribute cn
@400000004b21316a0e808834 <= get_ctrls: n=1 rc=18 err="serverSort
control: No ordering rule"

That unfortunately is not defined in the core.schema
# system schema
#attributetype ( 2.5.4.3 NAME ( 'cn' 'commonName' )
#       DESC 'RFC2256: common name(s) for which the entity is known by'
#       SUP name )

I am sure there is a good reason why cn does not have an ordering, but
I am guessing it used to have this in the distant past since this
previously worked. So how would I go about changing the system schema?
Or does anyone have a better way to deal with this.

(I know I could play with client registry (kb) article but I would
like to handle this server side)

Thank you for your insights.