If you keg, you can try filling the carboy with CO2 before racking your beer into it. That way you have no oxygen and nothing to worry about. If you don't keg, then I'm not sure what you could do.
I personally wouldn't like that much headspace, but if you're careful and sanitary, I can't see it being a huge issue unless you're aging it for months.
He who drinks beer sleeps well. He who sleeps well cannot sin. He who does not sin goes to heaven.
Another HERMS rig...