Get a Seasucker bike mount. Uses suction to mount to your car. I drove from New York to North Carolina and back with one on my Insight and it's solid as a rock. MPG takes a bit of a hit but not terrible.
The good news is I got the bike in the back. The bad news is I have been riding primarily on the flats and my current location is pretty hilly and I have neither the legs nor gearing for it. That will, however, not deter me from riding. I just have to be a little strategic about route choice. Bonus is that all my route roads are freshly paved so those 23 slicks are rolling very nicely.