Just get the emergency tire and keep it inflated to spec. I think it is possible for a real one to fit in there if you don't have the Styrofoam tray under the floor board. If I did that, I would want the exact same wheel and correct-sized tire. The real wheel/tire is going to be much costlier, heavier and bulkier than the emergency tire, but as long as it fits under the floor board, I don't see why you couldn't do it if you feel like you have to.
Well, there you go - can't be done. I'm sure you can find a good emergency spare at a wrecking yard. But for the love of God, please get it off the car ASAP if you have to put it on. I see these people driving out on the Interstate at 80 MPH with these things and they are going to get killed.