I had this problem and solved it by following method:
use your own log4j jar instead of one that provided by jboss. Do it by excluding jboss org.apache.log4j jar module from your application (exclude it in jboss-deployment-structure.xml) and add your own log4j jar file in lib folder of the .ear package.
Now put log4j.xml in the root folder of your module.
By this method you have full control on log4j (like standalone applications).
let me know if you need more help.
Sample jboss-deployment-structure.xml for excluding log4j.jar:
<jboss-deployment-structure xmlns="urn:jboss:deployment-structure:1.0">
<deployment>
<exclusions>
<module name="org.apache.log4j" slot="main"/>
</exclusions>
</deployment>
<sub-deployment name="MyEjb.jar">
<exclusions>
<module name="org.apache.log4j"/>
</exclusions>
</sub-deployment>