I read on another blog that some folks use a lady's headband worn across their mouth, with cutouts to hook around their ears. I see Cobaltsky has tried the same thing successfully.
APPARENTLY They are about 3" wide and sell on Amazon, 5 for $5. I have some on the way.
Obviously the lips popping open is due to air pressure. What's odd is that the pressure is not constant. IE sometimes i can open my mouth and there is no pressure there. Not sure what that means or how that could be! Another mystery of cpap.
See post 2 above.
Works wonders for me, which to be honest, surprised me, better than tape alone.