You might want to look into AOA rotating internships at hospitals with well known (good rep) ACGME residency programs. For example both UMass Medical and UConn have AOA internships within their programs. They wouldn't be dually approved per se (I would imagine since ACGME isn't going to regulate the OMM content of such an internship), but the fact your coming out of a good name ACGME institution should negate the issue of being "less competetive" for specialties.