$> tree
.
├── pom.xml
├── symbolic-link-to-sources -> ../src
└── target
    ├── maven-archiver
    │   └── pom.properties
    ├── project-1.0-SNAPSHOT-sources.jar
    ├── project-1.0-SNAPSHOT.jar
    └── surefire

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-source-plugin</artifactId>
  <version>2.2.1</version>
  <configuration>
    <includePom>true</includePom>
    <includes>
      <include>symbolic-link-to-sources/**</include>
    </includes>
  </configuration>
</plugin>

<plugin>
  <groupId>org.codehaus.mojo</groupId>
  <artifactId>build-helper-maven-plugin</artifactId>
  <executions>
    <execution>
      <phase>generate-sources</phase>
      <goals>
        <goal>add-source</goal>
      </goals>
      <configuration>
        <sources>
          <source>../common/src/main/java</source>
        </sources>
      </configuration>
    </execution>
  </executions>
</plugin>
<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-source-plugin</artifactId>
</plugin>