years ago, I had to brush on the same paint I had spray painted on before, mainly touching up spots I had missed.
Due to the job, I needed to brush the paint on at several different times, so I decided to simply spray the acrylic paint (cheap craft store brand) into an old jar. I just kept spraying into the pot till I had enough and then closed the lid.
The paint kept for as long as I needed it, which was several weeks. I had used up the paint in the jar before it dried out, so I can't tell how long it would have kept, but when closed airtight, I suppose it would have been a respectable time...
Basically the same method, but a lot more paint was involved than in that link. Oh; and I did not use straws or blue-tac; I just sprayed straight into the jar from a little bit above the opening to prevent the propellant from blowing the paint back out of the pot again. I never bothered with letting the propellant breathe out of the jar though...