SApermrejectsave to a variable directory?

Is there any way to have SApermrejectsave use the rcpt_to as
part of the directory path?  I have a number or users for which
I provide a virus/spam filtered email address that forwards to
their real address.

Rather than bitbucket items that are being rejected, I'd like
to let those users see what's been rejected, so they can whitelist
if need be.

I've tried this:

SApermrejectsave: /var/exim/spool/SApermreject/$local_part@$domain

...but it doesn't work, since I see this:

root@spot> ls -l /var/exim/spool/SApermreject/
total 1
drwxrwx---    5 mail     mail          120 Feb 12 13:21 $local_part@$domain


fixes appreciated :)

-- 
--------------------------------------------------------
Dave Lugo   [email protected]    LC Unit #260   TINLC
Have you hugged your firewall today?   No spam, thanks.
--------------------------------------------------------
Are you the police?  . . . .  No ma'am, we're sysadmins.