SNS3Guppy
Are there not two doors just behind the flight deck on most freighters? Parachute harnesses could easily and comfortably be worn, just tighten the straps before use, with the parachute packs in quick-grab bins at the rear of the flight deck. Two big snap-hooks - takes mere seconds.
You are right, of course, the aircraft would need to be de-pressurised and relatively slow. That should not be too difficult to achieve, given the alternative. Adrenaline is amazing stuff.