It's easy to expire the request.session dictionary via request.session.set_expiry(seconds_until_end_of_day) or via SESSION_COOKIE_AGE.
But how do I set the expiry of a specific session variable? E.g. I've alloted an unauth user a temp_id. I need this temp_id to cease to exist in 30 mins. What's the best, most performant way to achieve that?