Como configurar o repositório do plugin local do maven 3

Eu preciso ter um repositório maven completamente offline devido a algumas limitações. De acordo comhttp://cwiki.apache.org/confluence/display/MAVEN/PluginResolutionException , só<pluginRepositories> são procurados por plugins. Então, eu estou querendo saber como configurar o maven para procurar plugins em um sistema de arquivos local. Eu tentei usar o prefixo "file: //" ao definir<url> mas não funciona.

DEBUG] Verifying availability of /home/dsun/.m2/repository/org/apache/karaf/tooling/features-maven-plugin/2.3.0/features-maven-plugin-2.3.0.jar from [central (http://repo1.maven.org/maven2, releases=true, snapshots=false, managed=false)]
[ERROR] Plugin org.apache.karaf.tooling:features-maven-plugin:2.3.0 or one of its dependencies could not be resolved: The repository system is offline but the artifact org.apache.karaf.tooling:features-maven-plugin:jar:2.3.0 is not available in the local repository. -> [Help 1]
org.apache.maven.plugin.PluginResolutionException: Plugin org.apache.karaf.tooling:features-maven-plugin:2.3.0 or one of its dependencies could not be resolved: The repository system is offline but the artifact org.apache.karaf.tooling:features-maven-plugin:jar:2.3.0 is not available in the local repository.

dsun@localhost:> ls /home/dsun/.m2/repository/org/apache/karaf/tooling/features-maven-plugin/2.3.0/features-maven-plugin-2.3.0.jar
/home/dsun/.m2/repository/org/apache/karaf/tooling/features-maven-plugin/2.3.0/features-maven-plugin-2.3.0.jar

O settings.xml

<settings>      
<offline>true</offline>
  <profiles>
  <profile>
    <id>local</id>
    <pluginRepositories>
      <pluginRepository>
      <id>central</id>
      <url>file://${env.HOME}/.m2/repository</url>
      <releases>
        <enabled>true</enabled>
      </releases>
      <snapshots>
        <enabled>true</enabled>
      </snapshots>
    </pluginRepository>
  </pluginRepositories>
   </profile>
 </profiles>
<activeProfiles>
  <activeProfile>local</activeProfile>
</activeProfiles>

<localRepository>${env.HOME}/.m2/repository</localRepository>

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