[Mimedefang] return smtp reject to remote server but continue to deliver locally?

[Chris F]

Here's what I want to do...

if (spam) then
  return smtp reject to remote server
end
deliver mail normally

The key is that I want to lie about rejecting the message to the remote
server.  In filter_end I want sendmail to return a permanent error code
like action_bounce but also want sendmail to continue to deliver the
message like action_accept.

Can I do this?  If so, how?  Sorry if this is a FAQ, but I doubt it is. 
The reasoning behind it is...

In order for bayes filtering to remain current and accurate it's necessary
that the message actually continue to be delivered by sendmail.  The
message will be directed to a suspect spam folder through header
modification and procmail.  Once processed by procmail the message appears
as if it was not mangled by mimedefang in any way.