Another option is a transatlantic J return (JFK-MAD or MIA-MAD) on Iberia, assuming you can find availability.
To minimise the fees, you'll have to transfer your Avios from BA to Iberia. If you book Iberia via BA you'll get stung with high fees, if you book Iberia via Iberia you won't.
You'll need to open an Iberia account, earn 1 or more Avios in it (use their shopping portal to make a cheap purchase) then wait 90 days before you can transfer though.