Multi-JSF support has been introduced in the latest nightly builds of AS7, which you can get from here https://community.jboss.org/thread/167590. Stan, who implemented this feature, has blogged about the details here http://jsfunit.blogspot.in/2012/11/multi-jsf-is-here-use-any-jsf-in-jboss.html. For those of you who are curious about what multi-JSF support is, here's an extract from Stan's blog:
Multi-JSF is a JBoss AS feature that I've wanted to implement for a very, very long time. Basically, it allows you to use any JSF implementation as if it were the impl that ships with JBoss AS. This works with almost any version of MyFaces or Mojarra. You can even install multiple JSF implementations and tell each app which one to use.
Please read the blog for details and give it a try against the latest nightly builds and if you have any issues/questions, feel free to create a *new* thread with the details in this forum https://community.jboss.org/community/jbossas7?view=discussions.