[Wavytone]

Amusing you should mention this. Two thoughts come to mind.

My first thought is to shift the focal plane out far enough to put a star diagonal on the back of the polar scope then insert eyepiece as usual. Which entails shortening the polarscope tube. The reticle will have to be flipped or a roof prism diagonal used.

The other thought I had is why shove it up the polar axis, anyway. I can’t see any reason why it can’t be on a bracket that sits on top of the scope while you align it, then remove later. This would put it in a much more accessible place as well. I’m sure it would be possible to make a dingbat that fits the hole in the dec axis, and fits onto the tail of the polar axis and carries the polar scope on top.

If you follow this line of thought there’s no reason why it couldn’t be on the main scope provided you have a way of reliably setting the scope to -90 declination and there’s no cone error.

If you are into plastic 3D printing there’s another alternative.

1. Since the polarscope is small, remove it from the usual position completely

2. Fit a star diagonal in front of the objective folding the view by 90 degrees.

3. Make a dingbat that plugs into the hole on the dec axis and mounts the scope so that the star diagonal is facing the pole, with the polarscope sticking out sideways from the top of the dec axis which should be pretty convenient to view. As above have to flip the reticle.