Just a thought;
I know the MD-11F has a "cabin air off" switch.
When pushed it shuts off all airflow to the main deck, all the air from the packs is fed to the cockpit and courier station only.
This provides a sustained flow of clean air and aids in keeping smoke out of the cockpit, and even aft of the courier station smoke barrier.
Surely this should be possible in the 747F?
The cockpit door itsself has two blow out panels which open into the cockpit, they are hinged within the door and are operated (released) by vacuum latches.
Bearing in mind the difference in volume between the cockpit and the remainder of the pressure vessel.
A windshield blow out will have the entire volume of the pressure vessel passing though the opening of the door, whereas a cabin window blow-out will require only the cockpit volume to be relieved.
Ifix