Zend_Controller unknown Controller--response

Currently, in Zend, if a controller does not exist, the index controller 
gets called.  However, when that happens the index controller has no 
idea that it is being called as a default behavior and also has no 
access to the real controller trying to be called.  What is the best 
approach to take in order to be able to catch a non-existing controller 
and be able to look up the controller name trying to be called.
So, for example, if I call test/hello in the url, and the test 
Controller does not exist, I do not want to simply get forwarded to the 
index controller, because then, index controller does not no that test 
was really trying to be called, and there are scenarios where may want 
to perform certain actions based on the fact the test was being called.
I do not want to have to override the core functions in the 
Zend_Controller package, as this will lock me out of future updates to 
the package.
thanks,
nissan