[eluser]Clooner[/eluser]
It depends, do you want to enable $_GET application wide or just for a certain controller/method?
It's likely to already have a MY_Controller in place for other functionality. In that case add the two lines to the construct and you have application wide $_GET.
In the case that you don't need application wide $_GET simply call it from the controller construct or the method where you need to access $_GET.