[exim] Use more then one router to send mail

Hi!

I currently use one smart_route to send out my mails from exim.
I have do that cause sometime dns lookup fail to post directly on remote
host, my ISP do it better then my poor connection.

However today, my ISP Smtp goes down and Exim try to send out my mail
thrue this one in loop...

At this moment my ISP Smtp server is still down and I cannot send out my
mails.

Here is my configuration for my router:

smart_route:
driver = manualroute
domains = ! +local_domains
transport = remote_smtp
route_list = * smtp.isp.com


dnslookup:
driver = dnslookup
domains = ! +local_domains
transport = remote_smtp
ignore_target_hosts = 0.0.0.0 : 127.0.0.0/8
no_more

Thus, in this case, mails are trapped on the first router but if it fail
the next router is not tryed!

So the question is, is there a way to configure first router to force
exim try the next one if the first fail???

Thanks in advance for any helps.

Cédric MARCOUX
Belgium - Sprimont