I don't know of a tutorial, I'm afraid. With repeating data in InfoPath, a rule outside of the repeating group will set all instances of the field - so in the rules where you query your data connection, you could add another rule to set a field in your secondary data connection to some value that it would not currently be (so the rule would fire) and then leverage that rule to set each instance of the field to something specific. I've attached a sample that shows what I mean, sort of. Save it locally, right click & select design to open in design mode then preview.