Hiding Spamhaus key from replies

[Bernardo Reino]

Hello,

I currently use postscreen with postscreen_dbl_sites pointing to my 
instance of spamhaus.net. With postscreen_dnsbl_reply_map I hide the 
secret key from the server responses.

Now, I also have/had "reject_rbl_client zen.spamhaus.org" a part of my 
smtpd_recipient_restrictions. I want to change that to use my secret key, 
but I can't seem to find a way to map the server name to something else 
(to hide the key).

I've read about default_rbl_reply, and I believe that what I need is 
rbl_reply_maps but -- at least as of now -- I can't seem to be able to 
make sense of it :-?

How can I configure postfix to do like postscreen_dnsbl_reply_map but for 
smtpd?

Thanks in advance!