there is going to be little to no good way to mount it to the helmet, I’ve been there done that. The only thing that was semi-decent was the GoPro and that was because it was specifically designed to do so and had a solid mount to the camera from the helmet connection.
Don’t be surprised if you struggle, that’s why most people end up mounting their cameras on the bike.
To add to the issue of the helmet, it will take forever to align it properly as your helmet tends to face down as you’re riding normal and on top of that the footage get’s funny since your head moves around a lot to look around.
Here is an example of what I’m talking about.
Even nearly straight up (which you won’t be on a sportbike) the helmet still tilts down.
So when you’re mounting the helmet as it sits on your table you actually have to mount it facing UP not straight. It’s wierd.
Here is a better example of how tilted it is