By default the ClassLoader for WebApp is to load the jars in your WEB-INF/lib first. So if you have JSF2.03 there, will override those comes with server. Just use the class as you described. Were you having errors? How did you verify you are not using the right version of jars?
When I copy application and run jboss, I got exceprion cased by:
09:47:32,293 ERROR [[/ccms]] Exception sending context initialized event to listener instance of class com.sun.faces.config.ConfigureListener: java.lang.ClassCastException: com.sun.faces.config.WebConfiguration cannot be cast to com.sun.faces.config.WebConfiguration
class WebConfiguration is from jsf-impl.jar
not using the good jsf-impl.jar
Application works OK on tomcat, but I must deploy application on Jboss. If I remove my jsf jars from library, everyting works, but I can not remove my application dependencies. I can not delete them due to tomcat.