This is how I mounted my action camera, a Polaroid XS100i, a very nice and much cheaper alternative to a Gopro. WiFi, HD, waterproof, submersible, and takes some really nice video (there are multiple reviews on YouTube if you're interested in one). I wanted a mount that was secure, but I wanted to also be able to remove all the mounting hardware from the helmet when I wasn't using it.
The mounting pedestal is formed from Steel Stik epoxy putty; basically, I put masking tape over the helmet and squished a blob of it onto the helmet and formed it into the basic shape. It was then freed from the helmet by running a piece of thread between the mount and the masking tape; it pops right off (it helps if you rub a candle on the masking tape before you put the epoxy putty on). Files and sandpaper gave the pedestal the final shape. The threaded mounting holes were made by drilling recessed holes into the pedestal with a brad point drill bit, dropping in some #4 nuts, and cementing them in place with JB Weld. The top of the pedestal was then sanded smooth, and it was painted white to match the helmet. The pedestal was mounted to the helmet using 3M outdoor mounting tape.
The actual mount was made for a cheapie action camera from Vivitar; the action cam was pretty awful so I returned it, but the mount was relatively nice and came with various attachments. I had to adapt it (the knob to secure the camera was too short, so I had to make a new one), but it's a damn nice mounting system for 15 bucks; basically it's a GoPro knockoff. I peeled off the 3M adhesive from the mount, and drilled holes for the screws that thread into the pedestal. The mount then attaches to the pedestal with #4 screws.
Because the pedestal is larger than the mount it has more surface area for adhesive, and provides a more secure base for the camera than the mount alone. It's stuck to the helmet like an alien face-hugger.
There's no denying that it looks dorky, but on the plus side, the color of the cam matches my helmet. It gives me a clear view above the windscreen, and I prefer having a helmet mounted cam, since it will look where I look. I didn't put one on to document my lack of riding skill; I just wanted to be able to record the cool things I see while I'm touring (I wish I'd had it when I went through Monument Valley a few years ago). The only thing left is a safety tether; still waiting for that from Amazon.