Here's an idea. What if each user could pay a monthly fee to block quotes from selected sources. I'd be willing to pay, oh, say 23 cents to block Jack Handey quotes. But I'd pay up to $1.88 to block quotes from Justin Bieber, Sarah Palin, and Gwyneth Paltrow. Might be a good revenue source for you.
(This is completely tongue in cheek. Thanks for the great work on this site and others).
“Be in love with your life. Every minute of it.” - Jack Kerouac