Add placeholder text on Parent Master

Is it possible to add placeholder text on the parent master? I want every single slide to have a textbox in the upper left in which I can indicate the section and lesson title for an eLearning module. Since I need 2 pieces of text that don't correspond to existing references, I can't just have it autofill the text reference, and since the titles differ in length, the textbox needs to be responsive to its text fill. 

It seems like the only thing I can do is add this placeholder text on every child layout, but this seems incredibly inefficient if I ever want to, e.g., change its location on the slide. 

MWE attached below.

Any ideas?