What you are suppose to do is setup the context (just like you would in a stand-alone version of Tomcat) in the jboss-service.xml file located under the jbossweb-tomcat.sar/META-INF/ directory. You will find this directory under the deploy directory.
I have tried this though without any luck. :-(
I too have tried with no success!
Hopefully someone can help answer this since one of my app. is not accessible right now.
I ran into this problem, and this is how I solved it :
I created the war exactly like in Tomcat.
I then created an ear that looks like :
$ jar -tf rubis.ear
The application.xml is the only other file which has the following :
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE application PUBLIC "-//Sun Microsystems, Inc.//DTD J2EE Application 1
RUBiS Session Bean implementation
And I can see the ejb_rubis_web in the right context ---
To change it, just change the context-root.