Well, you can go to "Advanced Search", switch to regular expressions at the top of the panel and enter, say,
or
in the "author" field. It is a workaround, a bit of typing, but it works and I use it quite frequently.
Disadvantage: a basic understanding of regular expressions is needed. But it is well worth to learn about regexp. You'll be a much happier Calibre user. It is one of the very powerful features of Calibre.
Regards, Mixx