I have heard of it a number of ways.
One is with a cut rate off peak meter, which is activated through a pilot fed contactor, another just disables the loads on the normal metered service in peak times.
Recently, Toronto and some other cities have institused remote A/C disconnects, which turn off yours and many others A/C on radio command.
I have seen a load splitter, which allows you to selectivley feed a large heating load or other intermittent loads. It would give preference to the other loads, and disconnect the heater to let the other loads use the same power.