[Simon]

I have no idea how to do this inside one WP blog, so I hope someone else can show you a way to do it. But since I don't know how to do it, I thought about how to get the result without knowing how.

I'm thinking it might be possible (but maybe too much work?) to do this by setting up a simple, stripped down blog for each camster. Each stripped blog would have just one category, their own "Diary of Camster" category. The standard post format could be edited to include the standard profile code for that camster. Then you could feed the RSS feeds of the individual camster blogs into your real blog, where they'd appear in the 'subcategories' where you want them.

Obviously, a custom-coded solution inside one WP blog would be ideal. So this is just a workaround suggestion in case you don't find another way.