[Exim] sender_verify_*callback rocks!

I'm going through the exim 3.22 docs to find new goodies and stumbled on
this:
sender_verify_hosts_callback = *:!10.0.0.0/8
sender_verify_callback_domains = *:!valinux.com

This totally rocks!

Yet, I may not be able to leave this on because having it on for 10mn showed
that it unfortunately rejects legimitate mail:
- web servers that send Email to subscriber lists but do not even have an
smtp daemon to receive bounces
- people who do not know about header sender masquerading and send mail with
header sender addresses that resolve in DNS, but do not point to an smtp
server.

I'm already getting quite a bit of pressure from users because I have:
sender_verify = true
sender_verify_reject = true
headers_check_syntax = true
headers_sender_verify = true
headers_checks_fail = true

However, I'm not the only one to have those on, so there is less legitimate
mail that's being refused by this.

Now comes the $10,000 question:
Is there any way to do verifies depending on who the receipient is.
In other words, if some user says "I cannot afford to miss any mail, even if
it means I get 3 times as much spam", is there a way to have the above
checks only active if the rcpt to: user is in verify_user_list or something?

Thanks
Marc
-- 
Microsoft is to operating systems & security ....
                                      .... what McDonalds is to gourmet cooking

Home page: http://marc.merlins.org/ | Finger marc_f@??? for PGP key