[Renate]

Mmm, you could make a Bluetooth keyfob with a thumbwheel.
You could even try it out with a Bluetooth mouse.
You could disable the mousy part if you like.
Of course your reader software would have to handle scroll.
I've used mouse and digitizer (like Wacom) on Android but I've not tried scroll wheel.

Whether the latency on eink would be too annoying or not is unknown.
On my current BT button keyfob I can flip back a half dozen pages in one (longer) click.

Looking through my code I see that I've experimented with joysticks.