Hi Dave,
The simplest thermo cut-off switch is two different strips of very thin metal (think of two sticks of Wriggley’s chewing gum sat one on top of the other). When cold, the current will pass through them keeping the connection. Each strip will expand with heat but different metals expand at different rates therefore the strip that expands faster will be bent by the other strip thus breaking the connection (if you see what I mean). Now, if you feel like indulging in a few hours of trial-and-error the could get the switch to work in reverse, that is to say as it bends it 'makes' a connection rather than breaks it, but to be honest, it all depends on how much fiddling you're prepared to do!