How can I install an app from the Microsoft Office Store in the desktop version of Excel/Word/... 2013 that does not have a Connected Service to the store?
Note this question isn't about how to link desktop office to the store, it's about how to get and use apps in desktop office in a business where policy says "do not link external services".
Another way of wording the question is "how do I download an Office Store app for offline install?"
The answer is: you can't get there from here. Thank you @Ramhound for asking the question that redirected my searches that eventually revealed understanding, even though it's not what I wanted.
The architecture of an Office "app" is predicated on active connection to an external server; see diagram. This is quite different from the "Add-Ins" I've used up until now (example) which follow the more traditional activation route of download files, unpack, install. My confusion was spawned in part by the fact that Microsoft also uses the "add-in" term for apps in the Store.
Manifest + webpage = an app for Office
The same Overview of apps for Office 2013 page that gives us the graphic above also outlines how to create your own file based Distribution Point repository from which to install apps. So it is possible, technically, to use app-add-ins without connecting to the Office Store service.
Practically it's not going to happen without support and commitment from the IT department and the developers of the app you're interested in. First with IT in order to set the trust relationship with the distribution point, and the server which the app is communicating with. Secondly with the developers in order to supply the raw app manifest file.
