Hi Steve,
Welcome to our forum! When I was at Microsoft, my team worked on Export to Excel back in V1 days and it hasn't changed significantly in SP1. I should be able to answer your question or point you to the right resource.
Exporting to Excel only supports using one table and all non-repeating leaf nodes, or just all non-repeating leaf nodes.
Couple options:
1. You could write some code to access the Excel object model from InfoPath form and programmatically insert the data into it. Might be some work, but you have the most control.
2. You could design an XML template for Excel. Bind the Excel spreadsheet to the XML and use the schema mapping tool in Excel to set up linkage. To use this option, you'll have to save the xml from InfoPath and open it using the Excel template. You'll also have to extract the schema from the InfoPath form to set up the mapping.
I don't understand your 2nd paragraph about "it couldn't be hard coded". What is "it"?
Patrick Halstead
Project Manager at Qdabra