This link contains a script to create the SD card - big health warnings that it needs to be adapted to your system or it could trash it.
In short, I think you have to have access to a LINUX/UNIX box with SD card interface. I tried to do this under Windows and failed immediately as Windows will not let you partition an SD card !!
I don't have such a box myself (although I have seen suggestions about booting Ubuntu from a CD-ROM) however "I know a man who can".
Will let you know how I get on.
UPDATE
OK - followed through the instructions (or at least my colleague did) and set up the SD card. Put it into the LLL and booted using Fn + Left Shift. Things happened as described, but instead of getting to a point where I could login, the existing window system kicked in for 10 secs and then went away (ie back to command line) with messages coming up that the LLL was going to close itself down.
Still boots as normal when NOT using Fn + Left Shift.
Not quite sure what to make of it all !!
