[exim] exiscan and spamd outage

sorry if this is off-topic, but I'm using spamd (spamassassin)
and have always been twitchy about the fact that when it goes
down, exim returns temporary failures to incoming smtp connections
(local senders still work, though that makes sense to me).

is there a way to specify in the config that exim should only use
spamd if available, otherwise proceed as normal?

(I recently switched to lmtp -> cyrus local delivery, so if I could
just get this last tweak in i'd be able to take down parts of the system
while letting the rest of it tick along).

--
Yeah, life is hilariously cruel. - Bender
Rasputin :: Jack of All Trades - Master of Nuns