There is no built-in way to get external data in the peek templates. They are HTML defined by the developer and this is what they show.
For a future version we intend to have a LiveTile and some methods for obtaining data for badges and perhaps peekTemplates (like webservice, wcf service) and exposing some events for the peektemplate but this is not available yet.
Perhaps now you can add a custom (and unique) CSS class to your HTML and use custom code to obtain external content (e.g. some form of jQuery ajax() request).
What I can suggest is that you share your ideas in our Feedback portal
so other people can vote and comment on them. If you like you can post the links here afterwards.
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