A Granite/Coral component PathField (granite/ui/components/coral/foundation/form/pathfield) provides a dialog box to select a path. Is it possible to set a default path to start from? I mean, something that can be changed by the user, not rootPath.
Have you considered using the value property? It's what the widget sets when you click through the content tree and select a page/resource. If you set this yourself in the dialog definition, the dialog should load with your path pre-set and allow the user to change it if necessary.