I am wondering if I buy another 06 Aluminum wheel & tire, will it fit in the wheel well under the trunk? Has anyone tried this?

When I got the flat tire in mine I was thinking of doing just that. However, when I tried putting the flat tire and wheel into the space for the spare in the trunk it did NOT fit, it was close but it was just too big. So a fully inflated stock wheel and tire will not fit.

But if you have a flat tire, you can store it in the trunk until you get to a repair place, right?

Yes it will fit in the trunk fine. It just will not fit in the designated place in the bottom of the trunk where the spare goes(the round hole under the trunk mat).