How do I get the Fn key to work on a Sony Vaio VGN-FS550?

I have both the sonypi and sony_acpi modules loaded, yet the Fn keys don't seem to do anything. xev doesn't report that any key has been pressed when I use an Fn-* combo that should exist, and Fn-* doesn't change anything if the key wasn't supposed to be an Fn key.

Also, spicctrl doesn't do anything; it reports that everything is 0 and won't change anything. I do have a /dev/sonypi device, and I can write to it, yet nothing works. There are the brightness and brightness_default files in /proc/acpi/sony/, but there is no fnkey file if that matters (read that somewhere).

What am I supposed to do to get these keys to work? I see the infrastructure exists to give them functionality, but they still do nothing as X won't even recognise that I'm pressing them.