That's a neat option buying what they should have given you in the first place, unless you're actually on a long trip and have suitcases.
What does roadside assistance do if you don't have a spare with no dealer nearby? I assume they transport you to a service station that puts on anything that will fit to get you going.
I realize RFTs are an industry issue, not just BMW, and I'm looking at a worst-case scenario that will hopefully never happen.