Yep this is in the manual.
Locate the "air bleed" wire behind the drivers kick panel, it's a plug with a single wire either side (usually green socket, white plug).
In my S1 Stagea its a very small black plug taped to a loom with a single yellow wire with a green trace going to the plug and a single black wire going to the socket.
Disconnect it.
Start car. As key comes back to the ON position, within 10 seconds, depress brake pedal 5 times, 4WD light will start flashing to indicate you are in 2WD mode.
You need to do this every time you start the car.
To go back to 4WD mode, turn car off, reconnect plug and off you go.
And if you plan to do this a lot you can put a switch in somewhere.
But if you plan to do a day's drifting better to remove the front drive shaft.