[exim] help with the router setup

I have 2 domains that are literally bombarded with email (at 1000s per day)
to the random local parts from 100s of different ips. While all emails
with non existent local parts are rejected, it does take a tall on
the production mail server. I decided to redirect all traffic to those domains
through the special designated mail hub that would filter all the mails
with bed local parts and let the only valid once through. One of the ideas is
not to use callout but have a local lists of local parts in plain text files (one
per domain). I did get the hub itself to work but I am having trouble to
setup the router to verify the local part. I have the following:

    hubbed_hosts:
  debug_print = "R: hubbed_hosts for $domain"
  driver = manualroute
  domains = "${if exists{CONFDIR/hubbed_hosts}\
                   {partial-lsearch;CONFDIR/hubbed_hosts}\
              fail}"
  route_data = ${lookup{$domain}partial-lsearch{CONFDIR/hubbed_hosts}}
  fail_verify_recipient = ${lookup{$local_part}lsearch;{CONFDIR/$domain}}
  transport = remote_smtp

But exim complains that fail_verify_recipient is not set correctly.
What do I need to do to get my idea working?