It would be difficult (if not impossible) for any airline to apply fuel surcharges to already purchased tickets.
Regardless of what some think, it would also be difficult (if not impossible) to apply a significant fuel surcharge (that may exceed the price of the ticket) to domestic purchased tickets. The current competitive environment in the U.S., unlike Europe, would not support $200 fuel charges. I don't care what some yahoo at the "revenue desk" said...