[exim] Exim - Force ignore of fatal errors from smarthosts

Hi,

I was wondering if somebody has found a solution for what I am trying to do,
currently I have a few ISP connections into my office, handled by my router
with automatic switch over if one fails etc..

Each ISP has it's own SMTP server, and there is no way for my mail server to
know which ISP link is currently active.

I've tried to set exim up by delivering to ISP1 and then try ISP2, ISP3,
etc... however as soon as exim gets a "relay denied 554" it gives up and
tries to bounce the message. How can I force exim to ignore the router in
that case and move on to ISP2 smarthost?

Currently trying:

begin routers
        relay1:
                driver = manualroute
                transport = remote_smtp
                route_list = * smtp.ISP1.COM

        relay2:
                driver = manualroute
                transport = remote_smtp
                route_list = * smtp.ISP2.com

I've also tried putting all ISP smarthost into one single route_list, and I
get same result.

BR,
Mike