You lot have been done - I've got a spacesaver in my 370
Its a 350 spacesaver - fits the well once the foam fill is removed and the Bose sub fits inside the wheel.
Jack and handle added and I also carry the torque wrench (you can see in the pic) for peace of mind. Fronts need 20mm spacers for the 350 spacesaver to fit over the 370 calipers but straight fit on the rear but as I run with the spacers on - no issue for me there.
Theoretically, if you got a front puncture you could put a rear wheel on the front (I have tried it and it works without fouling anything) and the then the spacesaver on the rear as an emergency get you home job but would not recommend it - carrying a spacer would be much better.
Yeah, I know about the extra weight but like Lee I would rather have a wheel to get me home, than rely on the puncture being a tiny hole that the gel supplied might fix but then I gather is likely to render the tyre u/s even if the puncture could be repaired.
Only reason the gel is still there is for when I come to sell the car, without the spacesaver most likely. The pump I find really good for the odd topping up, as invariably garage air machines are out of action