Well, sure you can access the variable in your main template if you declare it there. But then you won't be able to modify it in the "blob" template.
You don't seriously have "Use a variable in one template that's declared in a different template" in your business requirements, do you? I would expect that was more like how you decided to implement the business requirement. That's why I tried to find out what the business requirement was, that you decided to implement in this way.