As some of the more senior members may recall, I used to be able to control my mouth leaks without resorting to drastic measures like taping, glueing, stapling, or stitching the lips together.
Then as I lost a bunch of weight, I noticed that I had begun to mouth leak with small puffs of air. I suppose that I had lost some fat tissue around my neck and the throat geometry must have changed and I lost my envied ability to control my mouth leaks au naturel.
At first I resolved the leak issue as described in this post. Then, CraigP posted a similar solution using men's underwear elastic as shown here.
So CraigP gave me an idea to modify my system by using an ACE bandage (rather than men's underwear) and the remainder of the post explains how to do it.
Get yourself a roll of 2” or 3” wide ACE bandage (the one with clips though you will not use the clips, avoid the self-adhering type) and cut a piece about 8” to 11” long depending on your size.
8” for very small size mask headgear
9” for small size mask headgear
10” for medium size mask headgear
11” for large size mask headgear
When measuring for the cut, do so with ACE banadage unstretched in natural state. Then sew the ends together so that you end up with something like this -

What I do is basically wet my lips before putting everything on and then sort'a bite my lower lip as I slip on the ACE bandage.

I then put on my PapCap and chinstrap.

Then finally I put on my nasal pillow mask over the top and attach the hose to the PapCap with a velcro tie. It all takes less than a minute to get everything on and adjusted.

You can adjust the tension of the ACE bandage by gently pulling on the parts behind the chinstrap. The chinstrap has a dual purpose of holding your jaw from slacking open and also to keep the ACE bandage in place across your lips. Once all is adjusted, the upper lip is kept in place over the lower lip by the ACE bandage making an excellent seal. I wake up in the morning and my lips are slightly stuck together.
The cool thing is that if for any reason you have open you mouth to cough or talk or drink water, it is really easy to readjust everything back and quickly go back to sleep.
Hope it can work for someone else.