There is a locking tool that centres the rear steering rack and locks it so it can be calibrated. There is a bolt that is removed to insert the tool if you could determine the thread inside using a bolt you may be able to lock the rack perminantly. Then just disconnect the 4WS ECU. I have never tried this but it may be worth a go, as long as you don't turn on the ignition with anything disconnected you will have no problems. Hope this helps.