Originally Posted by Viajero
AFAIK that is one of the few unswered (untested?) issues yet to be settled in this forum. If memory serves, there's no post in the archives reporting either success or failure. So, go on, try it and break new ground!
.. and don't forget to tell us the outcome.
I'll bet that's one of those questions that'll get 12 different answers from 8 different airline agents. If you really want to do it, keep asking until you get a 'yes' and fly away happy. If you'll be in London to do the re-issue, you should have all the OW airlines to ask.
I'd book the segments first, then arrange reissue separately.