How to create dynamically controllers function name in codeigniter

[eluser]beeLoop[/eluser]
[quote author="Aken" date="1350371478"]Ahem...

[quote author="Aken" date="1350081544"]Use the 404 override controller method.[/quote][/quote]

Hey i didn't get how to achieve my requirement using 404 override controller method.
Put some more light how to achieve it using 404 override controller method.