How to add custom default bookmark to Gnome Files?

Is there a way to add a custom directory to the default shortcuts to Files' sidebar? Not as a bookmark, as a default XDG directory? For instance, I've added XDG_WORK_DIR="$HOME/Work" to .config/user-dirs.dirs to define a new 'Work' XDG folder, which seems to work as xdg-user-dir WORK does output /home/user/Work. However, it still doesn't show the 'Work' shortcut in Files. I've also noted that the default 'Templates' directory is also not shown, so I'm assuming these shortcuts are defined elsewhere - where? It would also be cool to add a specific folder icon as used by the other default shortcuts.