So I finally got around (avoided work enough) to looking at the K2 to see about custom screen savers. I used the 2.0.1 update binary and Igor Skochinsky's work to create a fake update and dump the /opt/amazon directory to the user accessible portion of the flash memory.
Things of note:
1) On the kindle 1 screen savers were raw 2bit images that were gzipped. K2 just uses standard PNGs.
2) There doesn't seem to be a way to add custom screen savers, but I'm admittedly bad at trying to disassemble java class files and figure out what's going on.
3) I was, however, able to create another update binary that does nothing but change the SCREEN_SAVER_DIR variable in /opt/amazon/ebook/config/framework.mario.conf from the default location of /opt/amazon/ebook/screen_saver to /mnt/us/system/screen_saver and this lets me put any PNGs I want into my system/screen_saver folder and have custom screen savers again.
Hopefully someone better at reverse engineering compiled java classes can figure out if there's a way to use our own screen savers without editing system files. But until then this method is working for me at least.