[Exim] spamassassin but not system wide

Hi,

I known the spamassassin thing has almost been beaten to death and I
know about the documentation in dman.ddts.net/~dman/config_docs/
but I still have a question. I would like to use spamassassin in my
.forward file, basically like this

    if <message is on some mailing list>
    then
        save $home/Mail/mailinglist
        finish
    endif

    <filter email through spamassassin>

    if $header_X-Spam-Status: contains "yes" ...
    then
        save $home/Mail/spam
        finish
    endif

    save $home/Mail/mymail
    finish

This is easy enough with procmail, but I don't see an easy way with
the exim .forward file. And I don't want to convert the entire
.forward file (which is a lot longer than the one above) to procmail.
Does anyone know how to get the above behaviour (not using spamassasin
system wide, and allowing some mailing lists to go through without
filtering to reduce overhead)?

Richard
--
We haven't figured out how to be lower priced than Linux.
                                Steve Ballmer (Microsoft)