Have JSF 1.2 two pages(one.xhtml and other.xhtml), that are included to the current page by following rule:
...
In addition to BalusC's answer:
Note that this only supports strings, not action methods. For the latter you would need to upgrade to JSF 2.0 and use composite components.
There is a way to do this with JSF 1.2, though it's somewhat ugly:
and