You should attach plain jar module as par to Ear Plugin - try it.
There is also something like jboss-packaging-maven-plugin with par support. This plugins allow creating par module - builds a deployable JBoss Process Archive.
Sample par project
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<packaging>jboss-par</packaging>
<build>
<plugins>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>jboss-packaging-maven-plugin</artifactId>
<version>2.2</version>
<extensions>true</extensions>
</plugin>
</plugins>
</build>
</project>