I need pages to potentially redirect, based on whether a session with a remote web service has expired.  I tried creating a child action and calling it first-thing in the template (view), but I get an error, "Child actions are not allowed to perform redirect actions."  How else can I make an Umbraco 5 page bypass rendering and instead redirect to another page?  This seems like a generic need, but I can't any information on how to do it.