I doubt it will work as the rolling radius of a proper space saver is the same (or very similar) to the standard wheel which means there is just sufficient space between the back of the seat-base and trim below the boot lid for it to fit; the collpasable spare has some free space around it and from memory it doesn't sit perfectly inbetween the two; also, the locating bolt may not fit. Best to phyically try one in somebdoy's car with a bracket before fitting! To be honest, I just left my 16" spare wheel loose in there, usually with something holding it in place. I did think about building a small frame to sit alongside it, put some MDF over it then carpet it in black.
No answer to my question on here, although a quick check with the parts team at the local stealership suggests the nuts come already-fitted into the big plastic tray and a new one is £106 (plus loads of blood swat and tears to replace it); I will fashion a DIY lash-up but to be honest it's secure enough with the two bolts already fitted plus the wheel through the floor.
David, unless you were already on a visit to see Mike you can always pop down to St Neots and we can measure out the hole in your boot as this is the bit that takes the most brain power, the rest is a cinch!