OK, thanks, I will give usbnet (and maybe kterm) a try.
The forum wiki for my KT2 I linked in my first post has "reginfo" in this format:
Code:
#Thu May 21 01:18:20 CEST 2015
givenName=A
userId=amzn1.account.AAAARRRRJJJJ4444JJJJKKKK7777
deviceName=B
userName=C
deviceEmailAddress=D@kindle.com
I assume that's current? It includes the "userid" line that bt4wang mentions in toothless' thread.