I'm sure it's technically doable, but is it realistic?
It'd be great to give advertisers the ability to block URLs.
I mean, Adsense PUBLISHERS have a big trouble trying to block certain mis-targeted URLs on a handful of pages on their OWN SITE which they know inside-out and monitor all the time.
The Adsense content network comprises of many millions of pages, e.g. just a couple of days ago I read "asinah" saying he uploaded "90.000 pages of fresh content".
Only an algo can take care of this problem. And the situation is 100% in Google's hands.