I'd assume that they would need to replace your rear bumper if you were looking to do this after you've purchased, so you'd probably be no worse off getting the tow bar attachment fitted as someone else suggested.
However, if you're getting the bike rack prep included as an option, then it saves you a sizable chunk of cash (£300 / $550ish in my case) when compared to the tow bar attachment option. The holes are covered by plugs which look similar to the parking sensors anyway, so they do not have an impact on the look of the car. Not sure if the ones in the link provided by Robert were done after the car was built, however the one I was shown was flush with the bumper, and colour coded with the rest of the car.
Hope this helps someone!