I installed 2 6x9's in factory position on the rear dash, then put an amp (up side down ) under the rear dash between them. I ran 2 RCA cables under the carpet to under the front seat, bought a XM Roady and when I wanted to rock I'd pull it out, plug it in the cig. lighter, throw the ant. out of the trunk on to the rear deck and rock. Easily stashed for that stock look.
I guess you could do the same thing with a stereo unit If you memorized the remote for it.
Also some guys install it in their glove box.
Jim