Yea, when I was in the ER suffering from severe W/D symptoms, they gave me a Zofran pill (gave me some to take home too, yea!) and they put a Clonidine patch on me (got a dozen or so of those too and they're supposed to last a week, yea!). I'd suggest trying to load up with as many "tools" as you can before the flight. Also, why not have a Dramamine on hand as well. I think they make you drowsy too which may help the time go by faster as well.
Did you mention how long the flight was? If it's over 6 hours, you're going to have some trouble with needing to redose, IMO. If it's more in the 4 hour range, you should be fine. Personally, I like pushing the limits of doing meds in unusual places. I wouldn't hesitate going in the bathroom with my backpack and do some lines of my Opana. If you shoot up and can do it in a decent amount of time, without freaking out (obviously very important - it helps to have a cool demeanor), I'd say go for it. I mean, it's not noisy or anything. I know if I were to snort on a plane, I'd have to time it with a flush (maybe running the faucet too!) or everyone would be able to hear me.