I know that what I posted works with the firmware level I had when I bought the card and using the CLI tools to set up the arrays, for the simple reason that I did it. However I didn't leave my card like that for long, simply because it doesn't suit what I use my arrays for.
I don't know whether the setup is possible with the current BIOS revisions, or if it ever was possible using the GUI tools (BIOS or OS based). I should probably have clarified this in my post. If I had a PERC not in active use at the moment I would check it again, although I don't have available hardware at the moment.
My apologies if my post is inaccurate or misleading. I will edit it shortly...