Pin single files to project

I'm working in a WordPress directory structure. For a project (usually a theme), the main elements I'm working with are one or two folders within the directory structure plus two separate files.

I'd like to be able to set up the project so that the two folders are pinned to the project sidebar and the two files as well - right now, when adding a file to the sidebar, the file gets openend instantly and is not pinned. Is there a way to do that?