Overfill the trunk, huh? I'm getting a mental image of a Cayman with half a bicycle sticking out the back with a red bandanna tied to the handlebars.
None of these cars are going to be truly practical. If we Americans had any sense we'd be willing to buy cars like the 1-series hatch or the old Z3 based M-coupe. I know plenty of us around here drool over them, but the population in general couldn't care less.
Side note - a friend of mine has a C5. He's 6'2 and his road bike fits in the back, just take the front wheel off. It's hilarious to watch him show up at a group ride.