Please don't be silly. You cannot physically cough hard enough with dropped O2 sats like that, and even strong healthy people will be unable to fully evacuate matter from lungs, especially biofilms. Next time you propose an alternative, provide actual data supporting it.
As a test, start doing it at say peak of a 2200 meter mountain. (That would be 90% with no acclimation.) See how far you can go.
Sleeping positions are irrelevant.
A positive pressure mask or cannula with O2 concentrator or supply is likely sufficient, not necessarily a full blown ventilator, and is much easier to sterilize. Still, it does carry risks. And it's the O2 concentrator part that's expensive.
Reduced efficiency and inability to evacuate matter fully (which you claim) does not seem to make the method useless. Severity of the condition is likely a spectrum too.
Not all cases are worst-case. Every person who can manage, through these techniques, a symptom that would otherwise need a ventilator, reduces the demand.
Sleeping positions are irrelevant.
A positive pressure mask or cannula with O2 concentrator or supply is likely sufficient, not necessarily a full blown ventilator, and is much easier to sterilize. Still, it does carry risks. And it's the O2 concentrator part that's expensive.