ex-MRU would mean the OP has to ticket with BA - be prepared for lots of extra fees. I think Gardy Loo worked out (in another thread) that you have to tag on about 18% of fees.

I'd go with the DOH idea. Besides the nightly visits to Bahrain on your own, you'd also get good TPs out of your Europe continent allowance with DOH-LHR.

I've no idea what the AA GSA in DOH is like with ATWs, but there's also a CX presence you could fall back on if the AA GSA wouldn't come to the party.

If your plans change to a DONEx - ARN has very good fares, and is much more accessible I suspect. AA GSA in ARN has also received rave reviews on here.

EDITED TO ADD: Here's an interesting way of issuing xONE3 ex-DOH if difficulties are experienced with any of the GSAs there.