domino and spamassassin

Hi!

Where can I find info for using spamassassin and domino. The problem is:
I'm not allowed to change the subject of emails and I'm not allowed to
throw emails away. The only possibility is
to add an additional header X-Spam-Level and let users filter by
themselves. But in Notes/iNotes/webmail there is no way to create a Rule
for that header. How can a user create Rules that filter for arbitrary
headers?

TIA,
  Andreas