The FiltaQuilla add-on supports regular expressions.

https://addons.mozilla.org/en-US/thunderbird/addon/filtaquil...

If you look on the authors web page it describes how to use either JavaScript or regular expressions in the search field.

http://mesquilla.com/extensions/filtaquilla/

Here is a related, tutorial-type blog post with screenshots:

http://www.digiblog.de/2010/11/regular-expression-mail-filte...