Using a controller as a 404 error page?

[eluser]chris613[/eluser]
I am also looking for such a solution. I was very disappointed to find that there isn't full CI framework support in error_404.php. I could redirect to an actual controller (http://ellislab.com/forums/viewthread/87493/) but that means an extra browser request and a change in the url bar which I'd rather not have.