If I understand your question correctly, then it ought to be a simple matter of creating special dummy backing beans for your pages, and then creating a test JSF configuration file mapping those beans to the .jspx files. The dummy beans, of course, won't touch any business logic or back-end services -- they'll simply be simple sets of data that will be easy to verify in your tests.
Create an ant script to substitute in your dummy backing beans and the test config file. Run your tests. If you don't want something as heavy as HTTPUnit, and if you're using Spring in your app, look at this blog post for an excellent way to mock up a full web context without a web server. Your tests will probably need to sniff the raw HTML output to verify the results. This is going to be tricky, because IceFaces loves to munge DIV IDs and other relevant parts of the DOM tree that you may want to sniff for. (This alone may be the reason why very few JSF developers try to unit test JSF output.)
Once your tests are verified, swap the regular beans and config file back into the app.
Voila! You've just unit-tested your JSF components.
Mind you, the whole business of swapping out beans and config files is messy. It would be much, much easier if IceFaces used Spring to match backing beans to JSF pages -- then you could simply define the test-beans in an application.xml with the relevant test classes. But such is life.
Good luck, and let me know how it works out for you!