This is probably old news but for an experiment I tried fitting the Olympus viewfinder magnifier ME1 and it fit and lined up. It was tight to slide on so some judicious sanding on the flange side of the ME1 is required for permanent installation. It must remain removable as it overhangs the film door.
I'll wait until I've shot some film before deciding on fitting one. It is a small but noticeable difference.
I just tested it again and non eyeglass wearers can just see the needle, eyeglass wearer couldn't hope to see the needle.
If you try this please don't force the eyepiece on with excessive force. It would be disappointing to crack the plastic flange on either the eyepiece or camera's face plate. It fit on my camera, it might break yours.