Download the jar and place it in your project src/lib. Now you can use the maven installer plugin.
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-install-plugin</artifactId>
<version>2.3.1</version>
<executions>
<execution>
<id>install-oracle-jdbc</id>
<goals>
<goal>install-file</goal>
</goals>
<phase>clean</phase>
<configuration>
<groupId>com.oracle</groupId>
<artifactId>ojdbc6</artifactId>
<version>11.2.0</version>
<packaging>jar</packaging>
<generatePom>true</generatePom>
<createChecksum>true</createChecksum>
<file>${project.basedir}/src/lib/ojdbc6.jar</file>
</configuration>
</execution>
</executions>
</plugin>
Now you only have to execute mvn clean once and the oracle lib is installed in your local maven repository.