As stated above, it all depends on the type of air conditioning system your Benz comes equipped with.
The fully automatic A/C system or "Automatic Climate Control" as M.B. calls it (code No. 581) is much less flexible than the regular A/C system (Code No. 580).
With the 581 you could get the system to throw you "some" cooled air to the foot wells, but only if the system wants to do it. With the 580 system you can get air to any position at the temperature you want, even independent temperatures to the left and right sides of the car.