Passing a value to an "+ add new entries" form

Passing a value to an "+ add new entries" form

I want to pass a value to an "add new entries" form. Take for instance the forms in the Zoho help example app "Dynamically adding items to a picklist" 

Back when that example was created it wasn't possible but now we can configure a look-up field to allow the addition of new entries. Let's say I didn't find the state I wanted for the selected country and wanted to add it. Since the "State" form in the example has a "Country" field, I wouldn't want to have to select the Country in the State form when adding a new State. I would want the Country that was already entered in the Registration form to populate the Country field in the State look-up form automatically.

So, I know how to pass a value from to a sub-form, but how do you pass a value from a form to the form the "+ add new entries" gadget opens?