I have had some big industrial buttons similar to the ones I have seen on real German platforms lying about for many years so I decided to wire them up.
Both buttons simply connect the layout ground to an s88 port. Then in my layout software I just created an event that is triggered by that s88, and told it to shut off power if that s88 goes high...
It also activates a second event that announces that one of the emergency buttons has been pressed so that there is an audio feedback that the button worked.