[exim] AOL X-Spam-Flag: NO

AOL in their infinite wisdom has decided to add the header X-Spam-
Flag: NO to their outgoing messages.
Due to the way I have Spamassassin set up with exim this causes any
message from AOL to be considered spam.
Is there a way to strip the X-Spam-Flag: NO on RCPT before any other
processing is done?