It's easy enough to get maven to generate manifest classpath entries:
<plugin>
<artifactId>maven-jar-plugin</artifactId>
<configuration>
<archive>
<manifest>
<addClasspath>true</addClasspath>
</manifest>
</archive>
</configuration>
</plugin>
but I agree with Stuart. Moving library jars to the EAR/lib directory is much more manageable.
Also, the current maven-ear-plugin is pretty good at assembling correct EAR files this way too:
<plugin>
<artifactId>maven-ear-plugin</artifactId>
<configuration>
<version>6</version>
<generateApplicationXml>true</generateApplicationXml>
<defaultLibBundleDir>lib</defaultLibBundleDir>
<skinnyWars>true</skinnyWars>
<modules>
<webModule>
<groupId>${project.groupId}</groupId>
<artifactId>...</artifactId>
<contextRoot>...</contextRoot>
</webModule>
<webModule>
<groupId>${project.groupId}</groupId>
...
</webModule>
<ejbModule>
<groupId>${project.groupId}</groupId>
<artifactId>...</artifactId>
</ejbModule>
</modules>
</configuration>
</plugin>