arguments to procmail

I'm trying to get procmail -m to accept command line arguments, so far
without any luck.  The call is:

        procmail -t -f "$FROM" -m "$PMRC" "$GROUP"

I'm expecting $GROUP to be referenced within my procmail rc file as $1;
however, I'm getting the null string.  My rc file reads:

        VERBOSE=yes
        UMASK=037
        MAILDIR=/usr/pangaea/spool/mail-archive
        LISTNAME=$1
  
        :0
          $LISTNAME/.
  
        :0 e 
          .junk/.

The output I'm getting reads:

        procmail: [28262] Thu Feb  8 09:02:53 1996
        procmail: Assigning "UMASK=037"
        procmail: Assigning "MAILDIR=/usr/pangaea/spool/mail-archive"
        procmail: Assigning "LISTNAME="
        procmail: Assigning "LASTFOLDER="
        procmail: Opening ""
        procmail: Error while writing to ""
        procmail: Assigning "LASTFOLDER=.junk/26"
        procmail: Opening ".junk/26"
        procmail: Acquiring kernel-lock
          Folder: .junk/26                                              273

I can't pass in command line variable because that gives up setuid
permissions.

The docs show you how to have sendmail pass arguments in, but don't
show you how to reference them -- the only comment I can find is that
-a sets $1 and $m allows procmail to take "an unlimited number of
arguments" without ever saying how they are referenced.  If I use the
-a argument, $1 _does_ get set, but this is incompatible with -m.

So, how DO I reference those "unlimited number of arguments" in my
procmail rc file with -m?  This is procmail 3.10.

eric