You're right, 8che. I was only considering the theoretical case behind whether or not it would be possible. I'm pretty certain it would be possible but I admit to having no idea of how long the wheezing demand pumps would take to assist the electric pumps to do their job.
Most important is the engine failure case that you state. I, stupidly, did not think of that and, for obvious performance reasons, there's no way Boeing would certify the procedure; if not for any other reasons, then definitely for this.
I've never seen one but I've heard of a few South American approvals for operating above 8400'. I believe these are issued individually to airlines and clearly have specific procedures applicable to the airports they're operating from. I once spoke to a pilot from this region who operated a 757 and he considered me a sea level type of pilot as I'd only made it up as high as Bogota
