Mickjoebill: These bungee straps have been around for a very long time and have been used by photographers for both video and still shots from numerous helicopters all around the world.
I am sure however, that as TRC has said, these home-made arrangements (as you intimated) are not a certified accessory approved for aeronautical use.
However, as Hughes has pointed-out .. this does not mean that NAA's will not be willing to provide temporary approval for their use, they clearly do. I would hazard-a-guess though and say that many photographers/operators have not traditionally bothered requesting such approvals in the past.
I know quite a number of pilots who use GoPro's with the sucker mount on the exterior of the fuselage and my further guess is that NAA's probably won't say much until one escapes into the rotor-works (God forbid!).
As TRC says .. have fun .. and don't forget to showcase the fruit of your labour!