[exim] RCPT Address in DATA?

I'm want to use something like the following in my DATA ACL, but
(obviously) $local_part and $domain are empty. I've already made sure
there is only one recipient in messages with an empty sender in the RCPT
ACL, so that won't be a problem.

deny    message     = bounce messages must be returned to a BATV signed address
        senders     = :
       !condition   = ${prvscheck {$local_part@$domain}{BATVKEY}{yes}}

Basically prvscheck should expand to an empty string when given a
non-signed address, and "yes" when given a signed address. I don't want
to do this in the RCPT ACL because it could reject callouts. So I'll
wait until after the DATA phase so I know the sender really is committed
to sending a message.

Is there anyway I can get access to the full RCPT address while in DATA?