The bloggerdesign blog has this article on how to get custom feeds from your blogger blog. Basically, you use your labels to get topic specific feeds. The result is just the posts for that label in an atom format.
The basic format is:
Where blogname is your blogs name on blogger. The labelname is what
appears in the URL of your blog label page.
Here are a couple example URLs from the article.
Example URL: http://googleblog.blogspot.com/search/label/personalization
Example Feed: http://googleblog.blogspot.com/feeds/posts/default/-/personalization
This approach does not appear to work with FeedBurner, but I think I really only want to annoy folks with ads in my main feed anyway. :)