[exim] check for defer in acl

How can I determine if a condition returns defer?

I want to add a header based on the result of sender address
verification with the value being OK, FAIL, or TEMPFAIL.
I'm having trouble figuring out how to determine if the verify = sender
condition returns defer. If this is not possible, but it is possible to
determine if an acl condition returns defer, I could move the verify
into an acl.

I'm currently using this hack:
acl_check_rcpt:
  warn
    verify = sender/callout=60s,random
    message = X-Sender-Verification: OK

  warn
    ! verify = sender/callout=60s,random
    message = X-Sender-Verification: FAIL

acl_check_data:
  warn
    ! condition   = ${if def:h_X-Sender-Verification: {1}}
    message = X-Sender-Verification: TEMPFAIL

Thanks,
xn