For the purpose of cooling, just setting the thermostat to its hottest setting would be in effect "off" just about all of the time. Depending on the design/temperature range of the thermostat, this isn't 100% though.
If you want to be able to do both heating and cooling, it'd get a bit complicated since the above would be inverted for heating.
If you want to be able to do both heating and cooling, it'd get a bit complicated since the above would be inverted for heating.