Bandwidth monitoring for individual subdomains

This is a toughy - but I am using Apache and have awstats and webalizer, but these don't differentiate between subdomains (as far as I can tell). Ideally I'd like to be able to configure one of these to be able to show me the aggregate amount of bandwidth each subdomain is using (I don't need detailed stats) just to be able to figure out what is eating a lot of bandwidth at any given time.

Any suggestions? Client side stuff like piwik won't work - it needs to work directly with logs.