You can do it out-of-the-box if you add default values for the rows and then add a lookup which copies the values over based on position and an ID.
A slightly better approach is to insert just the number of rows that you need and have a rule on insert that copies the values from the secondary data source list based on an ID.
To do the insert requires a little code or our qRules plugin.
Easy to do though. We've demoed this a million times. You should just attend our Thursday webinar and ask your question at the end and I'll demo the technique.