Often with both thumbs over the bore.  

I’m not intimately familiar with the 1911 clockwork: 

IS THERE ANY MECHANICAL CONDITION OF THE LOCKWORK THAT MIGHT, IF A PART FAILS TO RELEASE OR MOVE, MIGHT INDIRECTLY PRECLUDE THE BREECHBLOCK FROM MOVING WITH THE BARREL TO THE REAR. For example, an interrupter or a lifter.

Before doing much else, I would get a small can of the gunsmith’s friend, KROIL penetrating oil and apply a little around the circumference of the barrel where it’s extension enters the receiver.  I would also, if feasible, remove the forearm and inspect the ring that traverses the magazine tube, to look for any corrosion. 

Let the Kroil work for 24 hours. Then stabilize the butt and try again. 

10-4.  Hard to tell much without seeing it but I’ve not had the experience of handling one and trying to cock it. If the magazine is empty, does the bolt lock open when you push the barrel in far enough to reset the trigger?

My 1955 Auto-5 set up for field loads still takes a firm grip and determination to push barrel into the receiver far enough to get the cap screwed back on. Pushing the barrel assembly far enough down to latch the breechbolt open requires resting the butt on the rug and putting my weight onto the vertical barrel.

As you say, he may not realize the amount of force necessary to compress the recoil spring all the way to the rear.

Just thinking about leaning over a 1911 with its butt on the ground to cock it and chamber a round, then losing my grip on a slick, oily barrel and causing a slamfire while my face is inline- with the bore — gives me cold chills. I’ve had occasions in decades past to examine 8×10 color evidence photos showing what an ounce or so of lead shot did to a human head fired from near contact distance. All you can say good about it is it was quick and likely painless.