Office Powerpoint Web Add-In Save State

I am trying to develop a Powerpoint Add-In. Therefore I created a Web Add-In, added functionality etc. Last problem remaining is the saving of the current state of the different instances. It should be possible to create various instances of the Add-In on different slides, but I want the state to be reloaded when the document is reloaded. Until now I was not able to find any property which identifies an instance of the Add-In. (Saving could then be implemented easily using the Office.context.document.settings)

Maybe someone has been running through a similar problem and is able to help. Thanks a lot!