I did it for the smart gunner HS, both Audio & Video, and plan to do this for the helmet camera as well.
Pictures:
http://s1217.photobucket.com/albums/dd383/frapet69/Aliens/SmartGunner/I did use a real Pentax lens, removed the internal lenses and added a sun filter.
A “pinhole camera” can be placed easily inside the hollowed resin camera body.
You can use a wire or a wireless camera, I prefer the wireless version.
The easier version would be to use an “action camera” directly without the Pentax lens, but I assume this is not what you are looking for.
When you buy a pinhole camera check they also include the battery clip.