This page talks about using JBossCache over a multiplexed JGroups channel. Note that you first need the JGroups Multiplexer set up and running in JBossAS.
Note that this is only possible in JBoss Cache 2.x.
Comment out the ClusterConfig attribute in your JBoss Cache config file.
Use the MultiplexerService and MultiplexerStack attribs to point JBoss Cache to the multiplexer service and the stack to use.
See the JBoss Cache User Guide for more details.