Sure it is possible. My guess what you're talking about is request dispatching. You coulduse a servlet that uses the RequestDispatcher to forward a given request to another given context/JSP. If you use jetty, you can deploy a WAR and specify in that WAR what virtual host names it should map to.
Boom. There you go.
My guess is really that he's talking about his jboss-web.xml file. We had one like:
which worked in JBoss-3.0.4 with Jetty but not in JBoss-3.2.1 with Jetty.
Maybe I should have added the error, which might be useful as well.
12:42:14,993 WARN [JettyService] Failed to parse descriptors for war(file:/C:/Java/jboss-3.2.1/server/passkey/tmp/deploy/server/passkey/deploy/ResDesk.war/38.ResDesk.war)
org.jboss.deployment.DeploymentException: Failed to parse WEB-INF/jboss-web.xml; - nested throwable: (org.jboss.deployment.DeploymentException: expected only one virtual-host tag)
... edited out for clarity...