Dunno whether this helps. If I do something like:
[root@(none) platform]# echo DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD > /dev/fb0
[root@(none) platform]# /mnt/onboard/.python/eink_update.sh
2048+0 records in
I get a screen where the top 1/2 has (more or less) what was on the screen before, rotated 90deg clockwise, and the bottom 1/2 is black.