fbgrab, or something based on the fbgrab code should do the job. QtE for Kindle uses something similar, AFAIK.
EDIT: Or not. fbgrab doesn't seem to support low bitdepth framebuffers.
It might not even be needed, we may have access to a way to get a ready to use fb dump in a more common image format, but I've never looked into this, so I'm not sure about that
.