redirecting outside the Content handler

[Brett Sanger]

I have a few AccessHandlers that I'd like to redirect the user to the
correct page to get access if they don't have it.  I tried
ErrorDocuments, but I have multiple layers of authentication, and
ErrorDocuments won't cascade.  So I'm looking at switching the
ContentHandler.  internal_redirect() won't work, since it only works as
intended inside the content handler.  Can I just override the currently
expected ContentHandler?  How would I do that?