Not if the ad scripts are mixed in with the content-rendering scripts, in which case you'll need to do some on-the-fly modifying of scripts. Host-level blocking still works for ads served from exclusive servers, but a lot of them are starting to realise that it's so easy to block and are resorting to more subtle methods.

That said, a new type of adblocker based on pattern-matching against a JS syntax tree would be pretty useful.