It takes a regular shifter cable just fine. It requires the long-throw shifter, one type of which I guess you already have.
The shifter is a two-part rod. The non-drive side you see is actually a pin-like piece that threads into the drive-side half that has the indicator chain on it (known as the "spindle" half). The two-part shifter allows the hub to change sun gears, and hence gives you the fourth/bottom gear.
The two shifter halves need to be threaded snugly together. It is possible to have the non-drive half of the shifter to unthread and fly out of the non-drive side while riding. You'll have a deuce of a time finding it if it does that. Just make sure it's snugly threaded together.