Allow commands which remove a copied item if the command exits non-zero

I would like to write a command which removes an item if a given python script returns a non-zero exit status. I'm trying to "filter out" items which are in my lastpass account ([script is here](https://github.com/rygwdn/lastpass-check)) so that they don't show up in my history. I'm thinking it could be a new option in the CommandWidget like "Remove on Failure".

It might also be nice to make these items not show up in the tray menu beside "Clipboard:" somehow..