WLS 12c - Installing Maven plugin behind a firewall

I have read the instructions for WLS 12c and using the wls-maven-plugin, but when I attempt to install using the following command:

 mvn install -Dfile=wls-maven-plugin.jar -DpomFile=pom.xml

I get the following:

[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building WebLogic Server Maven Plugin 12.1.1.0
[INFO] ------------------------------------------------------------------------
Downloading: http://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-plugin-plugin/2.3/maven-plugin-plugin-2.3.pom
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3:17.398s
[INFO] Finished at: Mon Nov 12 13:33:22 CST 2012
[INFO] Final Memory: 5M/61M
[INFO] ------------------------------------------------------------------------
[ERROR] Plugin org.apache.maven.plugins:maven-plugin-plugin:2.3 or one of its dependencies could not be resolved: Failed to read artifact descriptor for org.apache.maven.plugins:maven-plugin-plugin:jar:2.3: Could not transfer artifact org.apache.maven.plugins:maven-plugin-plugin:pom:2.3 from/to central (