There used to be ways of tricking the Kindle into
thinking it was registered (to enable collections in the event that no wireless was available), but I have no idea if any of those techniques will work (or are even applicable) on newer models.
https://www.mobileread.com/forums/showthread.php?t=87686
https://www.mobileread.com/forums/showthread.php?t=87336
Good luck.