A simple toggle switch, rated for 10A works well too. Drill a hole, mount the switch, and splice into the wire from where the cord connects to the thermostat.
BW, do you ever find the two thermostats acting independently would contradict what you're trying to do with the profile? I am thinking there may be times when you adjust the heat down on the TO to maintain temps, but the SC wants to turn on and add heat. Has that ever been an issue?
A long time ago, I measured the temps that the SC could attain, but forgot what they were. But if the SC can only produce say, 375F, then once the roast gets past that point the SC thermostat may never get cool enough to turn back on. Does that make sense?