Well, here in 'godless' Hiroshima, we bow to the shoumen only when there is a picture of the Founder displayed, or the Japanese flag. At the main dojo, where the chief instructor practises, there is no space for a picture, so we just bow to each other. If there were only one person training in this dojo, there would be no bow at all.
My own dojo is the judo hall of a local school. We 'transform' it into an aikido dojo by means of the picture and, of course, do a shoumen rei. Occasionally I train by myself, ukemi and suburi etc. Sometimes I put up the picture and bow to the Founder; other times I dispense with this and just get on with solo practice.
I certainly do not bow to reinforce a habit: I doubt whether the habit acquired from 25 years residence needs any more reinforcing.
Best regards to all,