What a great idea; I was thinking about trying the exact same thing last night!
You're bound to get some vibration with the mount off road so eventually the part of the camera I'd be most worried about would be the lens/optics/light receiver alignment. The electronics are quite robust and should be OK.
I think mounting the camera beside the rear wheel out to the side might give some interesting angles showing you pedalling, the front wheel etc.
I'd be interested to see how you get on with this. Good luck.