Adrian is right. you can piggyback right off of relay 4. you can also use any other open relay in your control box. Just be mindful of your voltages, for example my dust colector is set up to turn on/off automatically but because it runs off 110vac i needed a solid state relay. you can use SO x,1 to turn the relay on and SO x,0 to turn it off. X is the number of your relay. and if your really feelling spunky you can add those lines to the post processor!
"The most valuable tool I have is the experience of others" - Me