In command line interface I can modify default datasource of ee-subsystem with the below command.

[standalone@localhost:9990 /]/subsystem=ee/service=default-bindings :write-attribute(name=datasource, value=java:jboss/datasources/MySqlDS)

But in Web interface of wildfly 8, I can't see any sub configuration of ee subsystem on web browser. I suggest that i can modify datasource attribute in web admin console as i can with above cli command.