I get exactly that with CloudFront, a custom origin (with Sprockets), and appropriate HTTP headers. If CloudFront doesn't see a file, it asks Sprockets for it

I get exactly that with CloudFront, a custom origin (with Sprockets), and appropriate HTTP headers. If CloudFront doesn't see a file, it asks Sprockets for it and caches it however long I tell it to. You can do the same with Varnish if you don't want to use Amazon's CDN. Having run a large site with prebuilt assets for several years, I really enjoy not having to do it anymore.