--- Update ----
OK, the source/binary are available here. Right now, this is a command line Java application (which means much hassle for the less technically savvy). Also, you will need the Apache xmlrpc library (available here). I'm going to keep working on this, so let me know what you think.
For the less tech-savvy users: I am building a graphical interface that runs inside of a webpage to do away with installation hassles and command line.
So, once you've got the files downloaded, you can run it like this:
java LJReplace [username] [password] [search expression] [replacement]
The search expression can be a plain phrase or a regular expression.