Alan,
Unfortunately this is not currently possible. There is a new Feature Request for it on the Agile Central Ideas site at https://ideas.rallydev.com/ideas/D4489 I encourage you to add your comments and vote for this Feature. Of if it is not exactly what you desire, add your own.
As a possible workaround you may export the view a HTML and import into Excel. It is not perfect, but may help you out.
On the Portfolio Item page you may set the filter to the Portfolio Item or Epic you would like to see so it is showing the entire hierarchy on that page. You can then click on the "Import/Export/Print" button in the upper right corner. It is the little box with an arrow going out of it. Select "Print ..." then choose "Summary list of items with children" and click "Print". Once the print page shows up, instead of printing, right click and select "Save As...". It should have a name of "printContainer.html". You can rename it to something that makes a bit more sense and save it. Then open the file in Excel. It may have some image error messages, but should import. Not sure if this will give you everything you need, but, hopefully it is something that will help.
Michael