IMHO, the type of person who installs adblock isn't the type of person you can sell things to easily. They're decidedly anti-mainstream, anti-corporate, probably not particularly rich, etc.
So it's not just a matter of convincing their userbase to stop blocking ads, you'd need to tell their current userbase to go away, and invite a better userbase to come and click on ads.
Reddit created this problem by fostering a culture of anti advertising early on.
Reddit should probably just become some non-profit foundation like wikipedia and show begging adverts.