Yup - there are helmet mounts out there but they all seem to involve counterbalance bags of sand.

I was kind of thinking of just a manfrotto magic arm and/or clamp on the handlebars. It won't get those, sometimes crucial, sideways glance shots but it doesn't add more weight to your head.

Better still, if someone came up with a mini steadycam that you could handlebar mount and probably help, with the camera's vibration control, minimise juddering.