That's the issue here. I once heard Jack Sweeny, the publisher of the Chronicle, admit that to an audience of businessmen. Subscriber boycotts are good because they push their circulation numbers down, but if you really wanna hit 'em it takes an advertiser boycott.
The Republican Party may be a good place to start - urge its candidates not to take out any ads in the leftist papers, especially during the primaries. They don't lose anything since republicans don't read those papers anyway, and the ads they deny often cost 10-20 thousand or more.
The Comical just has "weekly free subscriptions" where they litter on peoples' yard to get those circulation figure up there again.