Originally Posted by
CPMaverick
I don't believe that you can get the upgradable fare in one direction only on ua.bomb. You have to call to get the upgradable fare in 1 direction only.
I would recommend calling anyway; you should be able to verify on the phone that your upgrade will clear, before you purchase, then process the upgrade afterward.
Of course, that does require a competent agent and they are in short supply...
CPMaverick is right that you can't force split fare codes on dot bomb. The one time I was in the OPs situation, I booked and held the ORD-LHR W fare, then called and had them change the inbound to the cheaper S fare. That way, I still got the online booking bonus.