Kobo

A jailbroken Kobo (NickelMenu with FBInk installed) can show a Still screen the same way the Kindle script does: fetch image.png, hand it to a framebuffer tool, sleep for X-Still-Sleep seconds, repeat.

FBInk draws a PNG straight to the Kobo's e-ink panel:

fbink -g file=/mnt/onboard/.adds/still/image.png

Adapt the Kindle script by swapping its eips -g call for the fbink -g call above, and its /mnt/us paths for ones under /mnt/onboard. Everything else, the If-None-Match handling, reading X-Still-Sleep, sleeping, is unchanged: it comes from the device contract, not the display hardware.

There's no Still reference firmware for Kobo; this page is guidance, not a maintained sketch.