[exim] System Wide Filter & External File

Hello,

I have the statement in a system wide filter:

if $h_subject: contains "spam"
or $h_subject: contains "whatever"
then
     headers add "X-Banned-Subject: Yes"
endif

Is there a way to place all the words I'd like to filter in a file so I
don't have to keep adding them to the "OR" condition? I was thinking
about something like this but it isn't working as I would hope.

if $h_subject: contains lsearch{/etc/exim/banned_subjects.conf}
then
     headers add "X-Banned-Subject: Yes"
endif

-Patrick