1. Install MMM-RemoteControl - https://github.com/Jopyth/MMM-Remote-Control
2. Add some custom code to the MMM-Remote-Control module to handle requests for turning on/off the motion device.

In MMM-Remote-Control’s node_helper.js module, you can find the “MONITORON” code:

if (query.action === "MONITORON")
		{
			exec("tvservice --preferred && sudo chvt 6 && sudo chvt 7", opts, function(error, stdout, stderr){ self.checkForExecError(error, stdout, stderr, res); });
			return true;
}

Notes:

• query.action defines a trigger word for the MMM-RemoteControl to listen for.
• exec() - executes a command on the OS
• The rest is for error checking that the external command executed.

In your case, we could define the following:

if (query.action === "MOTIONON")
		{
			exec("echo "motion_enable on" > ~/pikrellcam/www/FIFO", opts, function(error, stdout, stderr){ self.checkForExecError(error, stdout, stderr, res); });
			return true;
}

if (query.action === "MOTIONOFF")
		{
			exec("echo "motion_enable off" > ~/pikrellcam/www/FIFO", opts, function(error, stdout, stderr){ self.checkForExecError(error, stdout, stderr, res); });
			return true;
}

Any other ideas?