X-SA-Do-Not-Run problem

Hi everyone.  I'm using SA-Exim 3.1.  There are certain users on my system
that don't want their mail scanned.  I accomplish this by having exim insert
a unique "X-SA-Do-Not-Run" header into emails destined for these users.  The
problem is that when spammers send an email with multiple recipients to my
system and one of those recipients include the user(s) to be skipped, the
message gets the X-SA-Do-Not-Run header and all the recipients get the spam.
Is there a way around this?

Thanks in advance for any help.

Jeff