[Zope] ZPT & contents slot

If I create a macro which defines a slot called 'content', is there any way to have that slot populated by a file with a specific name if it exists in a folder? What I'd like to do is create a structure text file, in each of the folders A B C and have it automatically loaded into a content slot of a master template whenever the options A B C are selected. Can I do that, and if so how? I have spent all day looking at ZPT references and have no idea if what I'd like to do is possible. -- John