I have also heard that the goop can make a mess of the wheel & make removal difficult. I don't think it could hurt the rim its selt, it would just make removal by a non-expert tire changing place (we've all run into those) difficult & they might potentially damage the wheel.
given that a year's membership to AAA or similar service is pretty cheap & cell phone coverage is getting pretty universal, I'd not ever apply the goop solution to my wheels. you can either have a flatbed take the car to a dealer (BMW includes a little phone book with all the dealer in the US with each new car) or cal someone to help you out.
I'd just call home for someone to get one of the many extra wheels & tires I'm sure to have (I have a problem with having too many wheels
) and bring it to me with a jack & wrench & change it myself.
the stock (at least in other markets, US spec is unknown at this point) STi spare only works on the rear of the car (it doesn't clear the front brakes) but that just means that the tire replacement task is just a bit longer than otherwise.