Does the command "polkit-auth" show nothing? Try running as root:
polkit-auth --user user --grant org.freedesktop.hal.storage.mount-removable
Now "polkit-auth" should show you have the the authorization to mount removable media, and in fact I can. That may or may not be useful to you depending on how often you reboot, of course.
It's a puzzle, though, that in /usr/share/PolicyKit/policy/org.freedesktop.hal.storage.policy the error message "System policy prevents mounting internal media" is for fixed, not removable media.
For a workaround which survives reboots, you could try changing /etc/PolicyKit/PolicyKit.conf to include:
See "man PolicyKit.conf". I haven't tried this, though.
Of course, anyone using either of these suggestions should think through the security implications.