[Mimedefang] mimedefang passing username?

[Gerald]

How do you pass the user in user at domain.com to spamc with mimedefang?

I don't see where there is any way to tweak the mimedefang to do a per
user spamc call.

My production servers currently pass sendmail -> procmail -> spamc.
Procmail calls each spamc with a username option so that spamassassin can
check the database for custom user prefs.

Thanks in advance for and suggestions or pointers,

Gerald