[exim] stop spam by subject line

Hi,

I'd like to block certain spam by recognizing a certain subject line or
part of it. The check should take place in the DATA section before
accepting the mail.

How would you arrange for it?

Certainly by an ACL. Changes should be necessary once a week or on a
lower frequency, so editing exim.conf and reloading it wouldn't be too
hard. Much nicer indeed would be a file lookup containing lines of regex
for unwanted subjects:

^MAKE MONEY FAST$
ENLARGE YOUR P
GAIN THREE INCHES