Вот рабочие конфиги.

/usr/local/etc/PolicyKit/PolicyKit.conf:

<?xml version="1.0" encoding="UTF-8"?> <!-- -*- XML -*- -->

<!DOCTYPE pkconfig PUBLIC "-//freedesktop//DTD PolicyKit Configuration 1.0//EN"
"http://hal.freedesktop.org/releases/PolicyKit/1.0/config.dtd...

<!-- See the manual page PolicyKit.conf(5) for file format -->

<config version="0.1">
    <define_admin_auth group="operator" />
    <match action="org.freedesktop.hal.storage.mount-removable">
        <return result="yes" />
    </match>
    <match action="org.freedesktop.hal.storage.mount-fixed">
        <return result="yes" />
    </match>
    <match action="org.freedesktop.hal.storage.eject">
        <return result="yes" />
    </match>
    <match action="org.freedesktop.hal.storage.unmount-others">
        <return result="yes" />
    </match>
    <match action="org.freedesktop.hal.power-management.reboot">
        <return result="yes" />
    </match>
    <match action="org.freedesktop.hal.power-management.shutdown">
        <return result="yes" />
    </match>
    <match action="org.freedesktop.hal.power-management.hibernate">
        <return result="yes" />
    </match>
    <match action="org.freedesktop.hal.power-management.suspend">
        <return result="yes" />
    </match>
</config>

/usr/local/etc/xdg/xfce4/mount.rc:
...
[vfat]
uid=<auto>
shortname=winnt
# FreeBSD specific option
longnames=true
-L=ru_RU.UTF-8
-D=CP866
-m=0664
-M=0775
#пользователя не указываем
...

/etc/group:

# $FreeBSD: src/etc/group,v 1.35.10.1 2009/08/03 08:13:06 kensmith Exp $
#
wheel:*:0:root,iZEN
daemon:*:1:
kmem:*:2:
sys:*:3:
tty:*:4:
operator:*:5:root,iZEN
...