Replying to this thread rather than the other:
That guide to measuring the stud pattern is not accurate. All of the brands listed also have five stud patterns that are NOT 5x108, too.
More generally, You are over complicating things.
Go and see your nearest Volvo/European wrecker and tell them that you want a wheel to use as a full size spare in your P1 S40. You should even be able to try it on the car to prove it to yourself.
If you go for something non-Volvo (other than an XR5 wheel), then you will have to be very careful on the details like centrebore and offset and stud size and brake caliper clearance. The time and effort to get this right is more than the cost of just buying the correct wheel straight up.