Not sure I can help you there, Tom -- I have always found that an unstable dismounting manoeuvre myself, too. As a tandem captain I got in the habit of dismounting my end by putting my left foot down at the moment of stopping, then unclipping my right foot and swinging my right leg forward up over my handlebars to come to parade rest on the left side of the bike. This avoids fouling your right leg in the stoker's handlebars or, much worse, kicking her in the face with a steel cleat. I've taken to dismounting single bikes the same way for consistency. But no, I can't dismount gracefully while the bike, single or tandem, is still moving.