Have you considered adding padding to your camera backpack comprised of vibration isolating/dampening materials ?
There are many manufacturers who produce such materials, but as an example, you may want to contact
Sorbothane. Their website's
Engineering Solutions Showcase includes isolation protection solutions for NASA Space Shuttle cameras shielding them from the violent vibrations experienced during launch. ( I doubt your motorcycle's ride would be that hard )
They also offer an off the shelf
standard product line so you don't need to worry about funding a custom engineering project.