Sorry to hear about this all mate. I've had the same problem where it just does not add up. volvo supplies a non-conforming size spare only to say in the USA owners manual that using the spare will cause damage to the awd system, go figure. Even if you put on a full size spare with a different tread pattern the same end result would occur on their awd cars. The only illogical way to keep these things rolling with a flat would be to carry a right and left spare on identical rims with identical dimensions to your running wheels. My best bet has been a can of fix a flat. I'd use this over strapping a smaller spare on my 2000 v70r any day of the week. After all the rambiling, I think your just stuck, check your manual see if it gives the same warning, that'll be the back bone of volvos argument not to pay for it!