Will a full size spare even FIT under the car in the same space as the compact spare? My guess is, it will not! Otherwise your FEH would have came with a full size spare. In fact, it is my understanding, that the standard Escape comes with a full size spare, but due to the HV battery pack, there is no room for such a spare in the Hybrid.

Whatcha going to do? Carry it around behind your backseat? Or strap it on top?
Unless you live WAY out there, or go off-road a lot... seems like a waste of time, $, and space.

What about taking along a can of "fix-a-flat"? I use them on bikes all the time, but have not used on a car in probably 15 years. Not a substitute for a proper repair, but may get you by for the rest of your day, or whatever.
JMHO