I'm booking a trip for October LHR-ORD-LHR, which is coming up at £100 cheaper if booked as a BD codeshare. Only question is, how can I get the E+ seating, if I want to credit the flight to my BD card. If I book on the United website, I can reserve E+ now (since I'm 3P), then switch to BD for mileage at check-in, but how do I do that in this case? Any ideas?