Multi Select Menu

I am currently working on a app and I want to append an action to the Multi Select Menu for the file app. However I’ve looked over the documents and the code for the app. I for the life of me can not seem to figure out how.

Adding normal file action was fine, but looking at the code it appears to be hard coded list for the Multi Select Menu. I really would rather not have to modify the app to make things work for now to have things break during updates.