[exim] Failover if spamd fails

Here's what I want to do. I have several spam filtering servers and
every now and then spamd dies. And that causes the messages to queue up
until I fix it. Is there a way to pass the message on to another
router/transport if the transport fails?

What I want to do is if spamd dies and the transport returns an error -
hand it off to another computer.