Template Hierarchy

Hi, everyone!
I'm hoping someone can help me think this problem through. I'm using MasterPages and my structure essentially looks like this:
Root Public Template Content Template Video Template Private Template In the Root, I have a ContentPlaceHolder called "cphBackground." This CPH has some default markup that I want to propagate to the Public and Private Templates. To do so, I don't define a ContentRegion for cphBackground in those templates.
However, I want to be able to override this region in the Video Template. The problem becomes that, since I'm not overriding cphBackground in the Public Template, I can't set a content region for it to use in the Video Template.
Does that make sense?
Essentially, to do what I want to do, I'd have to define a content region for cphBackground in the Public Template and then recreate the markup that is in Roo ...