Is it possible to restrict Outlook Addins to specific Desktop Clients?

Question

We are developing an Add-in that need to run only for Outlook Desktop Clients for Mac. We have reviewed the documentation provide for Office Add-in development and though the manifest.xml file might be a good method to set requirements for which versions of Outlook and which clients were required to run this add-in but it doesn't seem that there is anything obvious to be able to achieve this. We could benefit, also, from being able to specify some kind of fall back URL to download the Add-in from in the event the original URL isn't available.