This will be usable "as is" by very few people because it is intended for a specific binocular and also a tripod, but I hope it will serve as an idea and a starting point.
That's why I've also packaged the Sketchup file so you can edit and apply it as soon as possible.
Also, the device is adjusted to my pupil distance and there is no possibility of further adjustment, but that's not hard to add...