I've just gone through this with the MD and gotten frustrated with the process.
You can fit a 195/65R16 wheel and tyre into the spare wheel depression and the floor will fit as normal (maybe a slightly higher level but less than 10 mm) so this looked like a likely solution.
The nice thing was that the rolling radius of such a wheel and tyre was within 4mm of the road wheels.
Two problems:
1. the only tyres in that size are commercial evidently but this didn't worry me as it was only going to get used as a spare, and
2. Would a 16 inch wheel clear the brake calipers?
You might think so since the tyre placard shows a 16 inch tyre size, but the local Bridgestone agent was good enough to find a 16 inch focus alloy rim that is supposed to fit the Mondeo but when tried on the front axle it fouled the caliper - go figure.
I have 17 inch spare for the MA which gets carried in the boot on long trips and this would be ok providing I fit 235/50R17 rubber to it to get the correct rolling radius but that will lift the floor in the wagon by 40 mm which is what I'm trying to avoid.
The space saver in the wagon is 10% smaller in diameter than the road wheels. I think that will require that the ESC is switched off irrespective of where it gets fitted and if the puncture is in a front tyre then the differential is going to get some work. My back of envelope calculations suggest it would be like driving on a circle of 17 metre diameter for as long as it is in use. That's close to 750 circles if the nearest tyre shop is 40 klicks away
So if I stick with the space saver and I get a front flat I'm going to be changing two wheels I guess - or I fit the new rubber to the MA spare wheel and carry it in the wagon load area - luckily the cargo fence in the load area will prevent it from bouncing about.
I have not given up on a solution, and if I find one I'll post it up. I'm going to investigate a steel 16 inch wheel (if I can find one with the correct stud PCD). It may have thinner section than an alloy which would give a bigger diameter in the wheel dish. The alloy that we tried didn't foul by a great margin, I think I only need a couple of mm - watch this space.
Cheers