Purchase or find a small clip magnet that is relatively strong. A clip magnet is used for closing bags of chips or cereal, but it has a magnet attached for holding things on the fridge. You can find these at most grocery stores, and test their strength by feeling how much force is required to remove them from a metal object.
Cut a piece of string about four feet in length.
Tie one end of the string to the clip part of the clip magnet.
Place the magnet on the Nordic Track's console, where the safety key had previously rested. You will now be able to turn on your Nordic Track. Attach the other end of the string hanging from the magnet to a piece of your clothing when using the machine. This will pull the magnet off, and shut the machine down, if you happen to fall.