This post is based on my current understanding, which could change and should be verified by independent sources. With that caveat, I'll proceed.
The issue the person is experiencing falls under the category of "complex" sleep disordered breathing, which is estimated to affect a not-insubstantial minority (some say as high as 20 percent, others give lower numbers) of patients with sleep apnea. Complex SDB is not well understood by the majority of sleep doctors, who don't know how to recognize it on a PSG and keep throwing CPAP at patients and then accusing them of being non-compliant when it doesn't work out. Complex SDB refers to people who appear to have typical OSA (that is, plain-vanilla obstructive apneas) but when they are subject to the pressure of CPAP, they start to experience central apneas and/or hypopneas. Google complex sleep apnea and you'll find plenty about it. I see that some people are now calling it "treatment-emergent central sleep apnea"--which seems like a more descriptive name--and you could probably google that, too.
Regarding the issue of CO2 and non-rebreathing masks, the objective, again as I understand it, is not to have a totally unvented system, but rather to displace the venting valve slightly further from the patient, so that instead of the venting taking place at the mask you now have a non-vented mask but a venting valve just a touch further down the tubing. This increases the "dead space" in the system--essentially, the amount of rebreathed air--and thus raises the level of inspired CO2. As the level of inspired CO2 increases, the level of CO2 gas in the body (usually quantified as PCO2) increases. Since even a small elevation in PCO2 can stimulate ventilation (under normal circumstances, an increase in CO2, not a decrease of O2, is the major driver of ventilation; it is CO2 that makes you feel air hunger when you hold your breath), the approach makes sense physiologically. Note that the objective is to raise the level of dissolved CO2 gas in the body (PCO2) very slightly, as that is all that is needed. We're talking about increasing dead space by something in the 50-150 ml range (i.e., 1/20th to 3/20th of a liter; which seems even smaller when you realize that tablespoon holds 15 ml). We're not talking about a totally closed system.
The full text of the original major journal article on this subject (from 2010) can be found here:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3014237/
A more recent article (from 2014) by the same person revisits this issue and also discusses other approaches. The full text is here:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3998090/
Another article by the same person from 2013 focuses on much the same issues but since the title contains the words "complex sleep apnea," I'm guessing (purely a guess) that the article may cover some of the basics more systematically, though I've not seen the article myself. This article is not available free on line (that I can see) but the abstract (introductory summary) is worth reading:
http://www.ncbi.nlm.nih.gov/pubmed/24136715
You can probably get a copy of the original article for free of for a small fee from the local library by speaking with the interlibrary loan specialist. They can usually get print outs of journal articles. But the abstract itself is very informative and it emphasizes that a key tip-off to the presence of complex SDB/treatment-emergent CSA is that the apneas and hypopneas tend to occur during non-REM (NREM) sleep, i.e., not during REM sleep (= more or less, dream sleep), which is when obstructive apneas tend to occur (because sleep paralysis, and hence airway flacidity, is most prominent during REM sleep).
Though all this is very promising, I'm not sure what the results are in terms of efficacy of treatment. If I'm not mistaken the author of the above-linked articles has found that simply increasing CO2 (via increasing dead space or by any other means) does not completely normalize breathing, and he is now using additional approaches, though I believe that increasing dead space has provided some, albeit incomplete, benefit.
This subject is complex but if you start googling and try to struggle through the journal articles you'll certainly learn a lot about the subject and, sadly, probably know much more than most sleep doctors, who seem incapable of recognizing or thinking intelligently and physiologically about complex sleep apnea. If you have complex sleep apnea, you'll really need to shop around and find an exceptionally well informed and thoughtful sleep doctor--a "thinker." Or you can try to see the doctor who wrote the above articles, in the Boston area.
I don't mean to bash sleep doctors specifically; the sad fact is that the majority of doctors in most medical specialities (and generalists, too) are not out of the box thinkers and they will not be up on things that are not already widely known and accepted in medicine.