I've discovered there is a surprising amount of room under the little flap that most helmets have at the back of the head opening. I have a bunch of the extra cable (what did they think people needed all this cable for?) under there, and I bet you could fit that pack under the other side. Mine isn't plugged into the camera, so it is under my jacket running to a bag on my hip, and the little battery pack sits in my armpit, barely notice it. Not a useful tip if you have everything connected on your lid though.