How to have any unavailable function names as index() get parameters in Codeigniter?

In codeigniter, How can i automatically take any unavailable function name as a URL parameter of index() ? Example. If i have index() and say_hello() in my controller i want to be able to 开发者_开发百科get some_param as URL parameter in index() when i call localhost/some_param, but also maintain calling localhost/say_hello as a function.

Check out the _remap() function:

http://codeigniter.com/user_guide/general/controllers.html#remapping