Wikipedia, about once a year, has those donation pledge boxes at the top of every article …they must be somewhat effective since they come back year after year …better keep them small though to avoid disheartening users. Maybe start small like this trending community line at the top of the user feed.
P.S. : Since we don’t want the user to get habituated it’s better if it’s just a few days once a year.

… is 11169622 …

Maybe 9 post out of 10 are deleted by the few checks I made manually …or am I missing something ?