In Visual Studio 2015 connected to a team project on TFS 2015, I can go to Team Viewer -> Pending Changes and I can see a list of files in my (local) workspace which are "adds" but have not yet been promoted to source control. These are listed in a hyperlink such as Detected: 121 add(s), 0 delete(s). When I click on this link a window is opened listing all of the added files where I can select all -> right click -> delete
How can this be done with tf.exe?
No such option in Tf Command-Line Utility Commands. The items you mentioned are Candidate Changes. If you add or remove a file outside Visual Studio, Visual Studio can detect the changes that you make and treat them as Candidate Changes. tf.exe can only detect the add/remove files inside Visual Studio.
You may try to use TFS API to achieve what you want, here is a blog should help you:
https://roadtoalm.com/2013/06/13/using-local-workspaces-promote-excluded-changes-with-tfs-2012-api/
