I had this exact same question a few weeks ago. I had beer in a secondary for five weeks with the better part of a gallon of headspace. You've got an airlock on it, correct? If you give your secondary a little shake, enough CO2 will come out of the beer to bubble up the airlock. So if your beer is under a "blanket" of CO2, doesn't seem like much bad can happen to it. I certainly wouldn't worry about it. Plus you'll probably only have your beer in the secondary a few weeks. IMO you'll be fine!