Cycling in Brisbane Australia
Maybe something like this ?
Not cheap, but there's an addon for extra bikes.
I was going to suggest exactly this type from the Thule range. Excellent racks and dead easy to put on the car... you just need a tow bar ball.
These ones are good too and have room for a number plate & built in lights (brake/indicator). Quality is top notch. The other nice thing about these carriers is that you can still easily access the boot!