The McLaren MP4-29 shown at the teams launch differed in Sidepod specification to the one shown in the video's that accompanied the launch (See above). From this it was fairly safe to assume that the physical item was a placeholder and the components used at the first test would actually be representative of the true specification. When the car arrived in Jerez it was clear to see that the items missing from the launch were indeed on the MP4-29.
The use of the Chimney's has also led to the shortening of the sidepod airflow conditioner's ahead of them who's job it normally is to protect that section of the sidepod from the influence of the tyres wake (especially in yaw). Their job is now aimed squarely at protecting the airflow structure designed to navigate around the sidepods undercut to the rear of the car.
This solution when considered just in terms of the Chimney's may not be ideal but when you stand back and look at both the thermal considerations and the overall aerodynamic structures it neatly ties up several problems.