It is not possible to set custom message composer on jca binding for outgoing messages.

This bug is symmetric to https://issues.jboss.org/browse/SWITCHYARD-1379 but it is not about incomming messages but outgoing.
org.switchyard.component.jca.deploy.JCAActivator in method handleReferenceBinding does not pass jcaconfig to created processor (should be probably done somewhere near line 242).

Therefore JMSProcessor can do only JCAComposition.getMessageComposer(JMSBindingData.class) on line 126 and therefore ignores custom setting of message composer.