When I was riding a lot, my hair was so long I could /almost/ sit on it, and french braiding was by far the most comfortable solution.

You'd need a helper (unless you have double jointed shoulders or something) - just divide your hair down the middle, french braid down the sides from temple to nape of neck, braid two tails, wrap them up behind the french braids and secure (bobby pins, tucking them under, flat clips, it doesn't have to look amazing.)

It keeps all that hair right next to your scalp, and you don't really have any visible if you put your helmet on carefully. It was sooo nice to not have an elastic digging into my scalp, and everything fit nice and snugly. I imagine with a hairnet this would be even more bombproof.

Hell, if I had the money to ride and show now, I'd do that with my boring shoulder length hair, just because of how tidy and nice it is. =)