Let me caveat this with both 'apologies if this is a stupid newb question' [cue half readership heading elswhere] and 'sorry if this is a stupid question' [goodbye other half of readers] but...

I want to book a multi city trip ex LHR with some internals in the US on AA, and would like to do this through ba.com ideally so I can get immediate MMB access etc - this doesn't to my eyes appear possible... Am I being dumb?

Also as an aside, I'm amazed to find the AA don't fly SFO-LAS. Want to fly LHR-SFO-LAS-ORD-LGA-[stop off]-JFK-LHR and am having do the SFO-LAS sector on another airline...