We have the “TN: Popular Posts” widget. Currently, it shows all popular posts, however, I could modify it so that if user is viewing a category page, the widget will show only posts from the same category. Would that solve your task?
Ok, please update the theme to the latest version 1.4.2. Then go to “Appearance > Widgets” and add the “TN: Popular/Latest Posts” widget. Now in the widget’s settings you will find a new option – “Category view” – try setting it to “Show posts from the same category only”.
Please give it a try and let me know what you think.