I'm (or rather the person who writes LSI's webBIOS is) an idiot.
The whole point of this thread was because I was battling with an LSI MegaRAID card on this Lenovo Thinkserver TD200.
I've now spent a lot more time on it, and found the functionality I originally thought was missing! What you'd think you need to create virtual drives of a specific size, is actually completed by running forwards and backwards in the WebBIOS screens using something called "Span Holes", creating drives of a specific size (which originally refused to allow me to type the drive size).
I'm now a happy bunny, and can confirm the LSI cheap SATA RAID cards now DO do what you want them to.
