Actually, this is already in our issue tracker (SG-7617 and SG-9945); I've added a new topic here:

https://smartgit.userecho.com/topics/12-/

How will that be different to the File table filter?

You are aware, that Stash does not work on files, but only on the entire repository?

In the Preferences, section "Tools" you can already configure tools. Isn't this what you are looking for?