Well, Crutchfield says that no stereo can fit into our dash opening, if I remember correctly. Yet, I've bought two Pioneer single-DIN units and they both fit in without problems.
I've been looking to do this myself actually, since I hate the unfinished look a single-DIN stereo gives the dash. If only the opening didn't have the rounded corners, I might not be hesitant about getting a new double-DIN screen or unit.