Another option would be Chase UR points, which transfer to BA. Even if you have a UR card that doesn't allow transfers (Like a Freedom) you can find trades on CC for 1 UR to 1.5 BA miles. You can transfer UR points to someone who has a Sapphire Preferred/Ink Bold and ask them to then dump into your BA account as well.

I really would recommend using BA points for this. I agree SPG points would be wasteful... but a good trade might make me consider using my SPG points.