meta backend and substring searches

[Armin Wenz <awenz@mtgnet.de>]

Is it possible to disallow a substring search without changing the schema?

A bit more background:
I set up a meta backend connecting to different servers.
Read access is only allowed for cn and mail and userCertificate.
For I don't want any user to get cn's or mail-addresses by a substring 
search I want to disallow it, so a user have to know the complete cn or 
mail-address to get the attributes. It can easily be done by deleting 
the SUBSTR filter in the schema.
But is there another way?
BTW: sizelimit 1 is not what I want.

--

Armin Wenz