https://bugs.openldap.org/show_bug.cgi?id=8485

--- Comment #12 from Ondřej Kuzník ondra@mistotebe.net --- There are not many things slapd can do that would work in the general case, but libldap could expose a callback as an ldap_set_option to interface with OpenSSL/GnuTLS and do the work that's necessary.

If you could update the patch to that effect, you can load a module that hooks in there and implements your requirements.