You can still do it but you would have to have your Porsche guy do the work ... 
Here is the info.. Reposted for you from the man himself Davis !
"Since you asked twice Bill, here's the scoop on that setup (pun intended).
I challenged Henry with duplicating the 911 heat/vent system so I could mix both sources (ambient & heat) to fine tune the temp since those 911 exchangers pump out big heat and it's tough to moderate it with just the cable lever, plus I wanted cool air as well.
His answer was to install a scoop under the bumper with large ducting up the inside of the fender well and into the cabin thru a shutoff valve, then into the blower assembly. The heat system also goes thru the fan assembly for boost and direction control.
With this setup I can have fresh air and/or heat directed at our feet or dash vents/defroster or a mixture of direction. Plus when sitting at idle I can boost the air flow from either source with the 3-speed fan. That means if we're in a summer rain shower, stuck in traffic and things start to fog up I open the fresh air intake valve and crank up the fan and direct the air flow to the defrost/dash vents and voila, we've got clear windows and cool air blowing on the passengers. The heat source which may not be needed is left shut. Pretty neat.
This obviously required a lot of plumbing under the dash but the lower dash valence that holds the radio and air vents covers everything nicely.
While driving thru Redding, Ca in September at 104F we kept the fresh air vent open with the fan off but directed the air flow to our feet and were very comfortable so this system is about keeping comfortable in hot and cold weather and works great!
I've used a lot of words to explain something fairly simple but I know this is a first for IM and as an option, one of the best you could invest in IMHO"