oh wait I just came across a whole lot of relevant stuff!!!!
There's a plugin you can get here
https://www.mobileread.com/forums/sho...d.php?t=220565 which does at least as good a job as the procedure I figured out last night, and probably is a whole lot more useful besides.
I also had no idea that Kobo uses a proprietary format which is now known as kebup.
Someone should stick this plugin and all the related info at the top of the kobo section of this forum!