It’d probably be possible to make it so that LJ-to-Google Reader could do that, but it’s not a priotity – the tool was designed to facilitate the reading of Friends-Only posts (in addition to regular ones) over on Google Reader, and, as http://community.livejournal.com/howto/40882.html states, the feeds you’re talking about don’t include any kind of protected posts.

A feature that might get implemented sometime would be OPML Export, which might fix your problem and would help more people, more thoroughly. Subscribe to http://blog.lj.abnib.co.uk/ to hear about updates like that one as they become available.