I do it all the time. (seven or eight round trips a year) I simply 'jumpseat' international provided that they have seats in the back. Buy about $30 worth of cookies and chocolates at duty free, give them to the purser and thank him/her for the ride. Try to go on the flights thats not full in the front. Sometimes it works, sometimes it doesnt. Still, traveling internationally for $30 is a good deal. If you are traveling alone, its easier.