There was mention on another thread that having the RTW ticket broken up into seperate PNRs and then adding the FF number to the appropriate PNR at checkin or whenever convenient would be a suitable way to handle this. Is this indeed possible?

It makes it easier if the program you are trying to credit to may have a language/geographical hurdle to overcome. I can't imagine getting credit into IB after the travel would be easy for an Australian who speaks 10 words of Spanish.