That fickle thing called DOF...
If it were easy to have sufficient DOF, we would not all be chasing after it all the time.
At the same magnification and f/stop, DOF is the same too, no matter how long (or short) the lens.
You could permit larger CoC's in your equation, but that doesn't change actual DOF.
Backing away, and enlarging more will also not increase DOF per sť. It will change how parts of the image look relative to another (i.e. show less difference in sharpness). But at the price of absolute sharpness.
I.e. the gain in DOF is not achieved by getting more sharp, but by reducing the sharpness of the sharp bit so that the difference with the less sharp bit is less obvious.
As the example shows, it works. But it also does not increase DOF.
If analog only, the only real way to increase DOF is the slit light method: move the subject through a very shallow 'plane' of light, positioned where the plane of focus is, exposing only the bit in focus.
The hybrid way, stacking, works, and is much easier.
Perhaps we analog photographers should not always want to be 100% pure?