[exim] Passing results of other tests to spamassassin

Running Exim 4.50 on debian sid using config based on standard exim (not
debian's) config.

I'm wondering how to pass results of checks done in other ACL's to
spamassassin, so I can apply a score to it instead of a "go, no-go"
check.

For example, in my check_rcpt ACL, I may have something like:

  warn    condition     = ${if eq {$sender_host_name}{}{yes}{no}}
          message = X-Spam-Note: No RDNS

Unfortunately, spamassassin doesn't see this since headers added this
way are not (or do not seem to be) added until AFTER the spamassassin
check in the check_data ACL.

Is there a way to pass additional info to the exiscan-stype spamassassin
check?