probably too late, but might I suggest using a kickstand like the SP4 with it's infinite positions, but alter the SHAPE, and add resistance so that it's stiffer / locked (in some way) at 90 degrees perpendicular to the back of the tablet.
Alterations to the shape are as follow, we make the end of the stand slightly shorter, so it's a trapezoid shaped stand, with the edge shorter than the hinge. As you can see, when this kickstand is in the 90 degrees position, the shape of the hinge will naturally incline the tablet, which will be better suited for reading, IMO. Also, the trapezoid doesn't have to be symmetrical. By making the trapezoid kickstand asymmetrical, we will have 2 portrait positions to choose from.
Just my 2 cents. Sorry for the terrible drawing.