I'm wondering if some of the simpler cache-busting tricks would force google update their cache. For example, somescript.js?v=201210221559.
From: googlebot(at)googlebot.com
User-Agent: Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)At Blekko we post process extracted pages of the crawl which, if they were putting content behind js could result in js calls offset by the initial access but 3 days seems like a long time. Mostly though the js is just page animation.
I just checked one of my sites which loads available delivery dates via ajax through the google cache, and yep, it caches that as the dates are when the cache was taken.