Thanks for the information. After posting the question, I decided to take a different approach. (There were other things I would like to see in the Kindle doc that I couldn't figure out how to automate at all.)
Instead of creating the document in Word, sending it to Amazon, and then using Calibre to get it in the Kindle and to store on the PC, etc., I've switched over to Sigil.
I now create the original document as an ePub in Sigil (with cover, etc.), and then use Calibre to convert it to MOBI so that the whole thing works on my Kindle.
Even if Sigil ever creates MOBI (or other Kindle format) files directly, I think I'll still be using Calibre because of the library features.
Thanks for writing it and keeping it updated. When I can sneak some money past "She Who Must Be Obeyed," I'll send some your way. I can't complain about SWMBO too much; she and my kids bought me my Kindle for Christmas.