What about John “I served in Viet Nam” Kerry?
He has so much talent and ability (just ask him), that he could serve in both positions and do just as good a job as he is doing now as Secretary of State.
This will be Obama's fourth Secretary of Defense (he will tie a record in that regard--Truman is the only other President with more than 3), but no African American, no woman, and no Iranian-born person has held the position, so Obama could get a three-fer.