Remove controller name for affiliate system

[eluser]Mantero[/eluser]
I'm currently adding affiliate system to my site.

currently my affiliate agent can use URL like this:

http://www.mysite.com/affiliate/mantero

'mantero' is affiliate id which is unique and dynamic

my problem is how I'm able to remove the controller name in URL and they can just use like this:

http://www.mysite.com/mantero

My appologies if this has been asked before..but I really could'nt find any solution for my exact problem

thanks in advanced