Just to add to the story and for what it's worth; In his book "The secrets of Aikido" John Stevens published a photo of O Sensei pointing to a kamidana (page 29). The foto is part of a series of photo's published in "Training with the master" by John Stevens and Walter von Krenner (page 82 - 83). One of these photo's can also be seen here:
http://zenwood.com/woodwork.html.
While these photo's were being taken O Sensei explained that this little shrine was meant for the Aiki cross.
Tom