I have found a kind of a work aroung to this problem. Not really a solution but it works.
Mount the PCE lens on a Nikon body, turn on the camera, set the aperture on the lens to a value that You will use, press the preview button on the lens such that the aperture closes to the value You set - then
Detach the lens from the Nikon WITHOUT turning off the camera. This way the aperture stays closed down and the lens can be mounted on the adapter / camera and will work on THAT ONE SET aperture.
Should the need for another aperture arise You repeat the proces. Thus your Nikon will be the worlds most expensive tool for aperture setting - that is if it just sits on the shelf while You play with the Sony.
It works for me with a 6-7 years old PCE 24 mm and a mechanical Nikon-NEX Fotodiox adapter (at €38) on the A7R2.