eInk readers tend to be very light these days so that helps a lot with ergonomics.
I'm fond of two-column landcape reading (via Coolreader or Overdrive, usually) so I keep both my Sony T1 and FireHD8.9 in their cases with the cover folded back, letting the weight rest on the upper edge of my left hand and I stabilize with the pinky. The Sony I could keep it there for days on end if needed. With the tablet the pinky starts to complain after 5-6 hours.

Still, it works.