This isn't exactly what the OP wants, but when I convert epubs, or any other format, to AZW3 for my kindle, I search for blurb by downloading metadata, choose the best, then choose a cover. After this, click the Structure Detection tab and put a tick in "Add metadata at beginning" then convert.
This puts blurb at the beginning of the ebook. But you do have to open the ebook in order to do this. Personally, I don't find this a hassle because my kindle is still fairly fast, and I use Collections.
I don't have wi-fi, which probably disables some kindle abilities.
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