If I understand your question correctly, you want to add a list of user stories, and then add a set of tasks (the same tasks) to each user story. You could accomplish this by using the Excel Add In. Create tabs for importing user stories and tasks. Run the user story import, capture the new user story ids (you could create an export query on another tab of your spreadsheet to pull them out), then paste the IDs on your list of tasks, having the same set repeated once for each user story.