Thought some more feedback on this might help anyone else trying to do something similar. I just booked LHR>Asia, USA>LHR on a 241 no problem at all for a trip next year. After asking and reading on here for a while I wasn't sure If it would be allowed and was prepared to ask and If refused hang up and try again the next day. The whole thing only took 5 mins and the guy I spoke to on the BAEC blue line was fantastic. Very efficient.

Another cool thing was there was no domestic connections available at the time so I was prepared to call back in a few months and pay to have them added if anything came up. He said no I'll e-mail them and get them to release availability and phone you back once it's done. He said it usually takes about a week. Sure enough got a call back after 4/5 days and got the connections I wanted. Paid for the whole thing at that point.