There's a discussion of how this can be done at https://jira.jboss.org/jira/browse/JGRP-653.
The email lists for JGroups are at http://sourceforge.net/mail/?group_id=6081.
I would *not* (ab)use state transfer for transfer of large files. I know, some folks have done it this way, but I would not recommend it
The JBoss AS 4.x Farm service does file copy over JGroups; perhaps some of the code will be useful. The class that does the actual work of moving files over the wire is
This code uses the JBoss AS HAPartition, which for this usage is just a thin layer that calls through to JGroups' RpcDispatcher. You could code directly to RpcDispatcher. You can see how the HAPartition implementation calls through to RpcDispatcher at