I have a Mazda6 hatchback (with a spoiler like yours) that I have a bike rack for. It looks something like this:
The bottom part goes up against the license plate and the top part goes over the spoiler and up against the window. Since mine is a hatchback the top straps go above the rear window where the trunk opens. Works pretty good, although I do recommend putting something in the metal hooks that attach to the trunk. They'll slide around a bit and rub some paint off.