I chose uid/gid of 85 for this:

  /etc/passwd:avahi:x:85:85:User for Avahi:/dev/null:/bin/false
  /etc/group:avahi:x:85:

I guess rc.M is the place for this:

        # Start avahidaemon
	if [ -x /etc/rc.d/rc.avahidaemon ]; then
	  /etc/rc.d/rc.avahidaemon start
	fi
        # Start avahidnsconfd
	if [ -x /etc/rc.d/rc.avahidnsconfd ]; then
	  /etc/rc.d/rc.avahidnsconfd start
	fi

and then rc.K ??

        # Stop avahidnsconfd
	if [ -x /etc/rc.d/rc.avahidnsconfd ]; then
	  /etc/rc.d/rc.avahidnsconfd stop
	fi
        # Stop avahidaemon
	if [ -x /etc/rc.d/rc.avahidaemon ]; then
	  /etc/rc.d/rc.avahidaemon stop
	fi