I'm not 100% sure here, but...
When you upgraded to the 17" wheels and 225/45 tires you increased your wheel diameter by 1", but you also decreased your tire sidewall height by about the same 1", keeping the overall diameter close to stock.
This type of change is called "Plus 1". (If you had gone to an 18" wheel, it would be "Plus 2").
Therefore, I would think you'd be OK using the stock spare tire if necessary. (At least that's what I thought when I got my 17" Prodrive wheels.)
I'm sure someone will correct me if I'm wrong.