I'd love to hear about others' success, but it was precisely this "conjunction" issue that BA was unable/unwilling to assist with (despite both flights being BA into/out of LHR T5). While I agree with you that there must be a way to achieve "conjunction" of two separately purchased tickets, BA led me to understand that there was, in fact, simply no mechanism by which two tickets booked separately could be presented to be in conjunction with one another. [The two circumstances: 1. a purchased BA ticket connecting to a BA redemption ticket, 2. a purchased BA ticket connecting to a DONE5 issued by AA.] Hopefully someone else will report a better outcome (and will provide details and contact phone numbers for those of us who have thus far failed at this.]