substituting post id for parameter id

[eluser]msteudel[/eluser]
So I have a typical url parameter

/group/update/9

Controller: Group
Method: Update
id: 9


my update method expects the id as the first paramater

function update( $id ) {
// code
}

I was wondering if there were any built in functionality to support posting the id to:

/group/update

And still have CI pass in the id as the first paramater, sorta like using $_REQUEST instead of explicitly using for $_GET.

Thanks, Mark