Detecting lose focus events for Nifty TextField controls

I have used Nifty fairly extensively for a HUD but I’m now stuck trying to use it for a form to set some values. I’ve used TextField to create the fields and TextFieldChangedEvent to detect when the field changes value. Now I’m trying to add logic to update other fields when the user tabs out (i.e. the element loses focus).

I can see how to do this with normal elements (by setting the element’s controller with onFocus defined). But I can’t work out how to do this with controls (which already have their own controller defined).

Does anyone know how to do this? Is there an event I can subscribe to that detects focus change at the screen level?