@treaders: I just released an update package to install PoP's combined keystore (the one linked by GM) that *should* support every device out there

. See
this post.
AFAIR, there's possibly an older installer laying around for legacy devices, and ixtab's installer for the Touch, but there wasn't anything for the K4 (except the jailbreak itself), so, there.
Bonus points, that was a fun experiment to work on a clean KindleTool buildscript supporting the whole range of Kindle devices

.