Do you mean "tag a template with a session (hardcoded as jasonette action)" or "pass a value to a template"?
You can pass any value you want to a view or a template, describing a session, user's settings, contextual data, whatever. This way, if you build and store session values with other params, you can build your own system, even a time machine (navigating sessions, not "Back to the future" yet). Hope it makes sense.
May be I had kind of the same question as you, regarding views and templates.
There a new storage function coming that should bring more flexibility. Ethan is actively working on this and a GUI tool to help build $jason.