When you add a new CustomView you get this message:
Here, you can add it to the parent folder, you need to check it.
This is what LucaMs suggested.
Anyway in the other IDEs you need to load it with the relative link.
I understand your question, when you add the class the first time, if you add it to the parent folder it is not a relative link.
This is not a problem in most cases.
I have not tested how this behaves when you change the project name which is the parent folder.