HI Donovan,
This should be the same process as adding a repeating table from the Main DOM. When you create a secondary data source InfoPath creates a schema from a sample set of data that it pulls. If the sample set of data contains repeating elements then InfoPath creates a repeating stucture such as a repeating table or section. You might want to check to make sure that the sample data is repeating when you add the data connection.
What kind of data connection are you adding? Database, XML, web service?
Matt Faus / Microsoft InfoPath MVPQdabra® Software / Streamline data gathering to turn process into knowledge