Clearing smoke from the cockpit in case of a main deck fire, without opening an outside vent in the cockpit is not a big problem to design.
If you feed all the air supplied from the packs to the cockpit only, it will cause the flightdeck to be slightly more pressurized than the rest of the cabin, even when you completely depressurize the aircraft!
Its the same as smoking in your car and opening up one of the rear windows.
Even the slightest amount of air fed into the car from the dash-vents will cause the smoke to be drawn out the back-window.
Forgive me for comparing an a/c to a car but the idea should be clear.
It will not stop the heat from the fire doing its damage to the airframe but will at least provide the abillity to see the instruments.
I am amazed this does not appear to be possible in a 747, as its only a single switch in an MD-11.
I hope someone with knowledge of 747F systems can assist me on this one.
IFIX