I'm totally for it, but ditch the bicycle form, switch to a polycarbonate or other polymer based kayak-form, supplant the pedal-to-wheel system for one favoring a medium length wing comprised of the same materials we use to make stiff kites, keep everything mechanical, and we've got ourselves a plan. Though, you're thinking too base with helium. There's other means of lift, other substances that can be mixed to yeild a steady supply of lighter-than-air gases to provide lift. By adapting the hot air balloon chute system, you could control altitude and descent, and by using something like the zeppeling design instead of the balloon design, or a combination of the two, you could streamline so that you get more speed. You could coat the fabric in a lightweight epoxy resin solution, to stop people like our dear friends Cowbell40 and Neonbob from having at their devious fun. Wouldn't stop bullets, but if you were to carry some extra resin and some spare yardage of fabric, a quick patch should fix that, if it came up.