What most people do is to stash the factory radio behind/below newer one. There should be enough space there, you could try removing the faceplate if it doesnt fit.

And then, when you hook up your new one, use a T-harness to connect both radios to your existing plug. Crutchfield has the one below, and i'm sure there are others.
http://www.crutchfield.com/S-pkGL1qO...p?i=120701720T