Let's start with how Mercedes version works though, as it differs from the ones currently run by Red Bull, McLaren and Force India as they don't have the classis 'S' shaped ductwork attached to the front of the bulkhead, in order to move the flow from one region to another.
In order that Mercedes test this concept for its likely introduction on the W07 the team may have piggybacked their existing driver cooling method, so although it isn't as elegant as the aforementioned solutions it could help to validate the teams findings going into 2016.
These align with the heave dampers aperture but nothing has changed with that, this to me means one of two things, firstly they may be trying to maximise the airflow coming out of the damper aperture. Secondly they are not worried that the bulge will impinge on their findings, which means they are likely looking at making geometry changes to the front suspension for next season. This would have an effect on how acute the angle of the nose/chassis is, of which the 'S' duct can help the airflow to overcome.
Based on the configuration this iteration of the S duct it has more in common with the nose duct employed by Ferrari on the F2008 in my opinion.
Although I have given my intepretation of how airflow could move from the lower surface of the nose to the upper surface of the chassis, you should be aware that they may just be testing these components to see their aero drawbacks without everything plumbed in place.
Follows are a few additional image of the 'S' duct from Free Practice...