[exim] unblocking gmail

using

  drop    condition     = ${if isip4{$sender_host_address}}
          message       = blocked because $sender_host_address is \
                          in  blacklist at $dnslist_domain: $dnslist_text
          !dnslists     = list.dnswl.org
          dnslists      = dialups.mail-abuse.org \
                          : rbl-plus.mail-abuse.org \
                          : qil.mail-abuse.com
          logwrite      = REJECT because $sender_host_address listed in
$dnslist_domain

loses a lot of gmail as they keep adding outbound servers and they are
'too important' to update dnswl.

is there an efficient hack to double map the inbound ip to see if it is
google or yahoo?

randy