Yeah I can agree it's a horrible way to go out. It is possible, my wife went this way, she had been drinking but not excessively and not used pills but think you need very very strong will to see it through.
I've tried numerous times with this and always stopped before I manage to pass out as it gets very painful and very uncomfortable.
I've tried with pills, twice , where I took about 20 Xanax washes down with a couple of bottles of wine but both times I've woken up many many hours later with the bag on the floor.
I used an exit bag both times. My wife had tapped the bag to her head. I guess if you secure the bag very tightly and secure, then knock yourself out it would make removing the bag when unconscious more difficult . Either way there are better ways to go. Just pump in some inert gas