A little slight of hand may work. Hide the container field and use a a text field to represent your document. It can now contain any text you care to enter. You can still use scripts to insert documents and export them even though the container field isn't visible on your current layout. (This may take a second, hidden layout that you use for inserting documents depending on the insert method used.) You can even place a container field with a generic icon just above the text field so it looks like a document and its file name but really isn't.