How are you generating your redirect urls in your application? If you generate your urls only using the path (i.e. without a scheme/host/port), then they will automatically use the host/port of the original request.
Otherwise, you can manipulate the proxyName/proxyPort/redirectPort of the JBoss Web connector (see server.xml) which receives the requests from the load balancer. See http://docs.jboss.org/jbossweb/2.1.x/config/ajp.html