Strings to ON/OFF Toggle Switch without Rule


I have a tado smart themostat which is able to handle HEAT, AC,…
In my case I only need the HEAT and OFF options of that String Item, so I tried to map HEAT and OFF to ON and OFF via the stateDescription.
When i use the item with a list widget, i click the item and a popup with ON/OFF appears and everything works as expected.
But I would prefer to use the item with a toggle widget, but as soon as i switch to an oh-toggle-item it isn’t working anymore. What can I do to make it work with a toggle item?

String            Hvac_mode             "HVAC Mode"       { channel="tado:zone:bridge:office:hvacMode" , stateDescription=""[options="HEAT=ON, OFF=OFF"]}