I have always heard that you needed to be listed for the return early per TSA requirements, but I have no direct knowledge. Years ago, some posted you needed to be listed 24 hours prior. I think today, it's just somewhere around 2 hours prior as the list is transmitted 60 minutes prior to departure?

In any case, if listing and paying your taxes/fees on your outbound isn't practical, I've also used these methods.

1) call the normal reservation number and ask to make a "meal listing" so you meet the TSA requirements to be listed for your return. Then at your international, return airport go to the ticket purchasing counter (not check in counter) to pay your taxes and fees.

2). I've also landed at the international airport and gone up a level to the ticket purchase counter and listed/paid for my future departure. Note, this only works if there is a flight departing after your arrival. If your inbound jet is turning for the outbound and there are no other flights that day, the ticket counter may be closed.

3) in Paris and Frankfurt I've not done anything early, but simply shown up 2 to 2.5 hours early, gone to the ticket counter and taken care of it just at that moment with no prior listing.

All of my international Jumpseat travel has been post 9-11. YMMV, but with planning I've never had a problem.

Last thought, I have also "bought" two different airline taxes/fees "tickets" for returns as flights were pretty full. I wanted a backup. I checked in for both flights prior to security and told the 2nd carrier I might not show up if I made the first flight. Then, on return to the states I've refunded the one I didn't use. I've done that twice with no problems getting the refund.