How to add dependencies to a project run with jetty-maven-plugin

jetty-env.xml

<!--
  Example of data source configuration for Jetty 8
  -->

<?xml version="1.0"?>
<!DOCTYPE Configure PUBLIC "-//Mort Bay Consulting//DTD Configure//EN" "http://jetty.mortbay.org/configure.dtd">

<Configure class="org.eclipse.jetty.webapp.WebAppContext">
  <Set name="contextPath">/myapp</Set>

  <New id="MyDataSource" class="org.eclipse.jetty.plus.jndi.Resource">
    <Arg>jdbc/backendDS</Arg>
    <Arg>
      <New class="org.apache.commons.dbcp.BasicDataSource">
        <!-- Driver for Oracle 9i -->
        <!-- 
             <Set name="driverClassName">oracle.jdbc.driver.OracleDriver</Set>
        -->
        <!-- Driver for Oracle 10g and 11g -->
        <Set name="driverClassName">oracle.jdbc.OracleDriver</Set>
        <Set name="url">jdbc:oracle:thin:@localhost:1521:XE</Set>
        <Set name="username">myuser</Set>
        <Set name="password">myuser</Set>
      </New>
    </Arg>
  </New>
</Configure>

pom.xml

<!--
  Problem: your application needs a data source (let's say Oracle); you want to
  run it with jetty-maven-plugin by using 'mvn jetty:run'. Thus, you need the
  Jetty server to start with the database driver in its class path, but you do
  not want to add it as a dependency, because you do not want it added to the
  final packaged artifact.

  The solution is to add the dependency to the plugin itself, as shown below.
  -->

<plugin>
  <groupId>org.mortbay.jetty</groupId>
  <artifactId>jetty-maven-plugin</artifactId>
  <version>8.1.7.v20120910</version>
  <configuration>
    <scanIntervalSeconds>10</scanIntervalSeconds>
    <webApp>
      <contextPath>/myapp</contextPath>
    </webApp>
  </configuration>
  <dependencies>
    <dependency>
      <groupId>com.oracle</groupId>
      <artifactId>ojdbc14</artifactId>
      <version>11.2.0.3</version>
    </dependency>
  </dependencies>
</plugin>

How did your jetty-env.xml get injected into the plugin in POM?