If you want, you can just tap the wire at your actual brake light that reads 12v when your brakes are pressed down. Only problem with that is you gotta run the wire from the light to the cabin. Really not that hard if you know what your doing.
Or you can just make switch. One end to a 12v constant source, and the other to the wire from the remote start that requests to be tapped into the brake wire. If you do this, instead of pressing on the brakes, all you gotta do is hit that switch. IMO, if you choose this method, try hiding the switch.