[Exim] BACKUP smart host?

Question for you all.

Is there a way I can setup Exim so that it tries to send a message
directly, and failing that (4xx or 5xx received) it sends to a specified
host (aka smart host)? The type of logic I want is this:

message to a@???, c@???, and e@???

send to b.com's MX -> OK
Send to d.com's MX -> 550 Dynamic IPS not welcome
send message for c@??? to SMART.COM -> ok
send to f.com's MX -> 550 Dynamic IPS not welcome
send message for e@??? to SMART.COM -> ok

If that is possible please tell me how. I can figure ways to do a smart
host, but I cannot see a way to have a message tried again if a
transport fails using a different transport.

Thanks!
--
-- Dan