Fixed. The default can now be set in (standard)jboss.xml like this (this is the actual quote from the current standardjboss.xml)
<!DOCTYPE jboss PUBLIC
"-//JBoss//DTD JBOSS 6.0//EN"
"
http://www.jboss.org/j2ee/dtd/jboss_6_0.dtd">
<jboss>
...
<jms-resource-adapter>jms-ra.rar</jms-resource-adapter>
...