suppressing (No client certificate requested) from TLS header

[Julius Thijssen]

OK, I'm using SMTP with TLS, and I'd like to eliminate part of the
header it generates;

Received: from system (ip-address [1.2.3.4])
        (using TLSv1 with cipher RC4-MD5 (128/128 bits))
        (No client certificate requested)
        by mail.some.serverdomain (Postfix) with ESMTPSA id 75F61CA22F
        for <jul...@gmail.com>; Mon, 18 May 2009 14:35:22 +0200 (CEST)

should become

Received: from system (ip-address [1.2.3.4])
        (using TLSv1 with cipher RC4-MD5 (128/128 bits))
        by mail.some.serverdomain (Postfix) with ESMTPSA id 75F61CA22F
        for <jul...@gmail.com>; Mon, 18 May 2009 14:35:22 +0200 (CEST)

I'm already using
smtpd_sasl_athenticated_header = no
but I was wondering how to best remove the client certificate mention.

I'm already using maps/header_checks for some other header-removal stuff,
but this is a hard one. Anyone who has already done this using REPLACE
or something?

Thanks,

Julius