Not sure I fully understand your question. The "nested" part is throwing me off.
In IP2007, one of my feature requests made it into the product, which allows you to right-click a node in the data source task pane, and copy the full xpath for that node to the clipboard. This feature, unfortunately, does not exist for IP2003.
One thing I sometimes do, is to go into a secondary data source field, create a temporary rule where I can point to the field in another data source that I want the XPath for, then set it to reveal the entire XPath, which allows me to select it and copy it to the clipboard. Then I just cancel the rule. Maybe this will help.