[exim] General-purpose DKIM ACL?

Hi folks,

Chapter 56 of the Exim documentation includes two examples of ACLs
that check for DKIM signatures (see end of page):

http://www.exim.org/exim-html-current/doc/html/spec_html/ch-support_for_dkim_domainkeys_identified_mail.html

However, these ACLs only apply to specific domains. Is it possible to
construct a general-purpose DKIM ACL?

E.g. for every incoming message such an ALC would check if 1) the
sender domain has a DKIM policy record, and if so 2) whether the
message headers includes a DKIM signature, and if so 3) whether this
DKIM signature is valid. A warning would be issued if a DKIM policy
record was present, but a DKIM signature in the message headers was
absent or invalid.

Thanks,

Jaap