[Exim] call-out from command-line

I've been looking for a command-line option to let exim do e-mail address
verification via a call-out. Is this at all possible? -bv and -bt don't
seem to want to do it. I've tried using a custom config file with:

accept
verify = recipient/callout=10s,defer_ok

in the acl_check_rcpt ACL, but this does not make any difference.