[Exim] Removing spamassassin headers from incoming mail

Hi folks,

I'm noticing that it's trivial for a spammer to defeat my client spam
filtering rules.

My Exim w/ exiscan-acl server adds an X-Spam-Score header, which my
client filter then uses to test whether a message should be filed in my
Spam folder. I always include the X-Spam-Score, so that the scoring for
false negatives can be analyzed.

However, my filter uses the first X-Spam-Score header it sees. If
a spammer sends me mail with an X-Spam-Score that says the message
isn't spam, my filter believes that, because it readds the spammer's
X-Spam-Score header before it reads the one my server added.

I'm not hopeful, given that ACLs are run before routers and long before
transports, but...

Can I remove X-Spam-Score from incoming mail _before_ the ACLs add
X-Spam-Score based on the results of the SpamAssassin dialogue?

Ciao,
Sheldon.