[exim] antivirus and antispam integration

Hello,

I want to setup exim for virtual domains hosting using ldap as backend.
In addition I want antivirus and antispam checks.
>From what i can understand:
As antivirus policy is quite simple (remove viruses for every users),
antivirus at SMTP (using exim ACL) suits well.
But for antispam things are differents.
I want to use spamassassin (not very original...) and its user
preferences stored in the ldap directory (bayesian db and autowhitelist
in sql as well). If I am not mistaking... using spamc in ACL at smtp
time prevents system from using variable expansion such as
${local_part} or $domain... and so I cannot use user preferences.
Then I tried using spamc as a transport in exim:
It seems to work almost properly but I don't know how to deal with
spam-tagged message (I would like them to be delivered in a Junk Folder
but would like to avoid creating .forward files for my each of my users)
Does anybody knows how to achieve this goals?

Regards