Would a proper spare fit in the boot well?
Yes and no!
Diameter-wise it will fit, but depth-wise the alloy will stand proud slightly. This is why I will use it in conjunction with a boot install

I thought Jer had tyres with the alloys, but I'm sure we could work something out

So that would be :-
Me (Hurdy)
John (hufcforpromotion)
john_o
One unmarked alloy each
Maybe jer keep one himself as a proper spare.
I'll PM others to see what they are willing to buy at - OK jer?