Credit for the discovery goes to colleen c. Perhaps this was common knowledge but new to us: she discovered that the AirZound airbottle was just a glorified soda bottle, same threading. She was also messing around with her solution so maybe she'll post some shots later, but here is my final product.
I had an empty 1.5L bottle in the office so I gave it a shot.
It was a bit tricky to unscrew the cap, they used some kind of adhesive or sealant. I wrapped the cap with old tube and gently unscrewed it with a wrench. There is a thin rubber seal inside, watch for that, don't lose it. These water and soda bottles are apparently rated at 80-100 psi or more. I wrapped it with a fiberglass reinforced packing tape to lower the chances of rupture or effects thereof
Keep in mind that some bottles are weaker than others, the one I had seemed thicker and harder than most.
I'm going to stuff it in my front pannier, this is too much of a monster to carry on the bike and sure to draw cops attention It's been holding 90psi for couple of hours now.
EDIT: That wasn't any sealant under the cap, it was just some glue to prevent the cap from being easily unscrewed: it wasn't distributed evenly and was hard, too hard to be a sealant, so the rubber seal is what keeps it sealed.
Size comparison, it should give around 3x more capacity.