While this might be an acceptable option for some I have yet to see a place to hide the spare that I'd pursue - Pianewman's method is probably the best IMHO. You'd have to locate the proper spare at an acceptable price and still loose the large trunk storage of course. Now that I have the Modern Spare w/case and tools on hand I've moved it around a bit and considered and for me standing it up behind one of the front seats will work best. It's not secured but then again neither is my luggage, golf bag, or Yeti cooler so I'm not worried about the crash scenario. (makes me think back to the wooden tissue box flying off the rear window deck and killing the driver in the old driver's ed movie! But I digress
). I'll pack around it so it doesn't move while driving and press on. But that's just in my use case of course, others may have back seat passengers, etc.. I'll carry mine only on trips or if I decide to leave it in the car for day to day driving just putting it on the deck in the back will suffice.