[exim] Automatically dropping back to "smarthost" when relay…

I'm using the Debian exim4-daemon-light and related packages
(version 4.50-8). At the moment I have routers configured as
follows to deal with dynamic IP blacklists.

problematic:
        driver = manualroute
        headers_add = X-Warning: Your organization's mailrouter has been deliberately misconfigured\n\t\
                                 to force my mail through my ISP's unreliable servers.  Please ask\n\t\
                                 your administrators to stop blacklisting innocent broadband users now!
        transport = remote_smtp
        route_list = * smtp.blueyonder.co.uk
        domains = /etc/exim4/bastards.list

dnslookup:
        driver = dnslookup
        domains = ! +local_domains
        headers_add = X-DCL-garcia-router: dnslookup
        transport = remote_smtp
        ignore_target_hosts = 0.0.0.0 : 127.0.0.0/8
        no_more

########## The remaining routers handle addresses in the local domain(s).
...


The problem is that I have to add new domains to the "bastards.list"
*after* my mails to them bounce. Is it possible to configure the dnslookup
router so that if the host refuses to allow me to route my mail directly,
Exim will pass it on to the so-called smarthost and send a warning to
postmaster?

--
Thanks,
Adam