It would get distorted no matter how you did it, even if you projected onto a flexible media that could be stretched, it would distort by stretching your media.
maybe it would be possible to distort the image in photo shop so that when it is projected onto the helmet it would automatically regain it's perspective, similar to the anamorphic 3D principle, but I would imagine that this would involve a lot of work, it would certainly be out of my patience zone which on a scale of 1 - 10 is around minus 5.