In Europe there's a high-body 4 Door Wagon version of the Mk6 Fiesta called the Fusion. The early 2001 to 2005 model had some extra ducting that fed air from the heater box to the foot well of the rear passengers. In fact, there seem to be places in Europe that sell these after market to add them to the later Fusion. Ford FINIS part numbers for the centre are 1207466 for RHD models - 1207464 for LHD models - the tubing is different around the auto shift lever - then 1207474 and 1207475 for the left and right floor tubing. I am open to the possibility that these may fit the Fiesta. The parts may be difficult to get, but they look decidedly 3D printable to me....
Lukeyson