I notice there are problems with a lot of covers that hold (or don't!) or obscure the readers .
I may have an answer.
In the UK anyway, but I'm sure "globally" car accessories sell a small panel (6in x 3in approx) of self-adhesive silicone-y thin stuff for stopping things sliding on dashboards, like glasses etc...
It feels tacky/sticky but doesn't leave nasties behind, easy to peel off and refit, can be washed to renew adhesive qualities,can be cut to size/shape, and is, in general, A Good Thing.
And very cheap.........
So, a piece of this , whatever size you want, attached to reader or cover, will hold the device in place like...well ... glue !
It will work on practically any material, certainly metal or plastic, will work, as far as I can see, on any cover/reader. So you can buy the colour you want, cut off the bothersome straps, and away you go.
Kicks self for not "inventing" pack to sell to ereader owners !! :smack