In the scenario you describe, you're trying to isolate against one opponent in position. The hands I would do that with are good AA hands, preferably those with two-way potential, something like (A4)AJ or (AK)(A6); an A2 or A3 with a big pocket pair, like A2QQ or AK(K3); and what Steve Badger refers to as five-card hands, which consist of an Ace, a wheel card, a backup low card (no matter how high), and a Broadway card—not just a premium like (A2)(K4), but also hands as weak as (A46)J or A5(Q7).
Hands with big pairs can win unimproved heads-up. And five-card hands can make both some kind of high and some kind of low when an Ace hits the board, which is definitely an advantage heads-up. (For more on five-card hands, see
http://www.stevebadger.com/poker/omaha/secret/.)