I don't believe the way this used to work is possible. The Deft 5 ViewController now extends the Sencha ViewController class. Their ViewController works completely differently than the old Deft ViewController as far as creation, timing, event handling, etc. So we don't have any control over this any longer.
I'm not using Ext JS 5 yet (the projects I work on won't be upgrading for a while), but you might try looking at using a ViewModel to act as a relay. I believe you can specify ViewModel data when you're creating a view, and I believe that the ViewController has access to the ViewModel's data, so that might be an option.