Thanks for the suggestion! Currently the fixed upgrade offer for the TATL segments is 550€ each way, but the whole itinerary is currently sold for 1300€ return on the TP website, so I'd get a much better deal upfaring the whole ticket - hence my question. (And I don't think I'd be willing to pay 550€ for a 6-hour flight anyhow.) I guess I'll give them a call later this week and see.