[exim] custom redirect router question

I know this is probably a simple answer but I find myself lost and not
having a good solution...

What I have is an exim server strictly acting as an outbound relay.
What we're trying to do is if the sender's domain matches a particular
domain list, forward the email off to a catchall and not the destination.

I have a domain list that matches against domains in a file, thats
working fine.

The router I have set up is the following:
router_blocked_domains:
        driver = redirect
        senders = +block_domains
        data = blahcatchall@???

I know teh senders option is not correct because that is trying to refer
to an address list. I want to match the senders domain such as the ACL
parameter senders_domain = +domainlist.

I'm not sure where to go from here. Ultimately if senders email address
matches the domain list, the email needs to be forwarded to this
catchall and not the intended recipient.

Thanks,
James