So - the issue is that in InfoPath there is no rule based way to add an instance of a repeating group. You could do something with default data & conditional formatting - but you have to pick an outer limit of how many rows you'll allow. I'm attaching a sample where I've put that limit at 5 rows - but it could be larger if you added more instances of the group under Data > Default data on the ribbon. Save the file locally, right click and select design, then you can preview and try it. If this is going to be used in the browser, and if you will have a lot of rows in the default data, you should test it carefully - sometimes browser forms can be a bit more finicky than filler.
Hilary Stoupa
