This thread may help you. It shows how Jannik installed remote buttons.
I and some others here took a bit different approach. I have my router, LM power supply, and laser power supply all plugged into a power bar. That bar is connected to power through a paddle switch. If the stuff hits the fan, I can smack that paddle switch and everything dies. I used a magnetic one so that if it is tripped by a power failure, when the power comes back on, nothing re-starts until I hit the start button.