Unfortunately, for books bought from the Sony store, there isn't any way to change this behavior on the reader.
For books not purchased from the Sony store, you can change the meta-data using Calibre and then upload to your reader.
Personally, I've gotten used to using first name-last name for sorting, so that all my books (those bought from the Sony store and elsewhere) are consistent. I would like to be able to sort authors by the last name though. Don't know why Sony doesn't dothis by default.
dordale