First, you’ll need to make sure the following jars exist in %MAVEN_HOME%/lib (i include the versions i currently have):

• wagon-ftp (1.0-beta-2)
• commons-net (1.4.1)
• oro (2.0.8)

Then define a server (& its credentials) for the remote repo in your ~/.m2/settings.xml and finally issue something like:

 mvn deploy:deploy-file -Dfile=mysql-source.jar -Dclassifier=sources
     -DpomFile=mysql-connector-java.pom -Durl=ftp://my.server.com/path/to/repository -DrepositoryId=my.server.id