Email Forwarder w/ Condition(s) - Exim

I have a VPS w/ CPANEL (which I understand uses Exim for mail).

I would like to do the following:

Have a particular email account forward a copy of all incoming emails to an external email address. However, here's the catch: All email except those emails that are tagged spam by spam assassin. (for instance, have spam assassin put "spam" or similar in the subject)

How can I configure Exim to do this?

any ideas?

Thanks!
Shawn